From this I think we can infer that [the] optic nerve of fish is derived little from the anterior lobes, more from the walls of the hollow lobe, but not from the objects contained therein, and in particular the corpus striatum or optic thalamus, and none from the eminences situated externally and lower to the inferior lobe, because between this and the optic nerve there is no communication, and because there was no evidence of any alteration in the pathological cases.
In birds, although the primary origin of the optic nerve is the optic lobe [optic tectum], it is certain that the optic thalamus also contributes to its formation, as well as the peduncle of the brain with two or three fibers, the tuber cinereum, and the radiating lamina [optic radiations]. These (Table VIII, Figure 19a) descend along the flat surface of the cerebral hemisphere and concentrate in a nerve fascia from which a part enters the optic nerve before it joins into the chiasm; the other part, directed to the back circles the leg of the brain to then end in the external extremity of the optic thalamus, that in addition to being connected to the optic nerve, also finds itself in relation with the medullary fascia that proceeds from the cerebral hemisphere.
To clarify the nature and importance of the relationship of the optic nerve with the various structures previously discussed, I conducted several experiments. Of birds I selected the crow, because in addition to being a lively and strong animal, it has a soft skull that can be cut with a simple knife, thus exposing the brain without damaging any of its functions. Exposing a cerebral hemisphere, I raised with a probe the posterior and lateral part, and with a very thin scalpel shaped like a spear I touched and damaged the optic lobe, once in a transverse direction, and once from front to back. Every time that I made any soft touch the animal did not react, but when I tried to penetrate the substance with a needle, not only did the senses appear, but there were even convulsive movements, which I will discuss at another time. With respect to sight, I have verified that which the celebrated Flourens and others have observed, that is, a loss of vision from the opposite eye not only after a profound wound, but also from a small lesion, hence the integrity of the optic lobe is absolutely necessary for the exercising of this function. In fact, when the crow that sustained the above injury was allowed to wander, it walked as quickly as before, but ran at every step into the wall and other objects placed on the side of the damaged eye: a finger or other object placed near this eye was not seen, although the iris reacted normally. Kept alive for 2 days, the bird ate and maintained its usual lively status and quick readiness of movements, even though the brain hemisphere was exposed: the sight from the damaged eye remained constantly abolished. After bleeding the animal, we found on the right optic lobe a linear injury in the middle part of its superior surface that was deep two-thirds the length of the line, with small traces of blood on top of the damaged region. In other crows, using the same cautious procedure, I damaged instead the posterior part of the right optic thalamus above the optic lobe: the same result was obtained, that is, the loss of sight from the opposite eye, persistence of movements of the iris, normal movements of the entire body; in the sections we found the optic thalamus just barely damaged more or less next to the optic lobe.
In other crows I cut longitudinally into the ash-colored layer of the cerebral hemisphere close to the superior margin of the flat surface, and in doing so also involved the ash-colored mass that carries the fibers of the radiating lamina. The crows remained blind in the opposite eye, movements of the iris were maintained, as were the senses and movements of the body. The anatomical examination conducted after 1 or 2 days confirmed that the ash-colored layer from which originates the radiating lamina was affected by the cut for two-thirds of its length. Following up, I had a great desire to know what alterations would happen to the sight after transverse sections of the cerebral hemisphere at various distances from its anterior extremity. For that purpose, after assuring myself of the relationship of various points of the skull with the parts contained therein, I made, here and there, small holes in the skull, into which I inserted a slender spear-shaped scalpel, thus cutting in transverse a small portion of the anterior extremity of the cerebral hemisphere the size of two grains of rice put together: the animal showed no signs of suffering; when placed on the ground the animal was free and lively in its movements as if nothing had happened to it; however, the sight from the eye opposite to the damaged cerebral hemisphere was lost, but the pupils continued to move. Killed a day later, I ascertained the precision of the incision that I made. The same result was obtained with a not-too-deep transverse section either one-third, one-half, or one-fifth of the posterior section of the cerebral hemisphere. And even after removal of a small portion from the posterior margin of the cerebral hemisphere where it is pointed, the crow lost sight in the opposite eye. I would also add that the same lesion made to both cerebral hemispheres caused complete blindness without affecting other vital functions.
In other crows, I removed the right half of the dome of the skull, then cut the meninges, lifted the posterior cerebral hemisphere, and with two hits of the scissors I removed all of it: I immediately observed paralysis of the left side, but after a short time the animals recovered their movements, but the left eye remained blind yet the pupils still moved: the other eye saw perfectly. For the 2 or 3 days that they were left to live following the operation they were lively, they ate and walked normally. The section demonstrated that the hemisphere removed was that overlying the corresponding optic thalamus. I also decided to cut in transverse the anterior eighth part of each of the cerebral hemispheres: this was followed by a complete loss of sight, but the pupils remained mobile. The crows were doing nothing other than jumping, hitting everything they encountered. When I removed both hemispheres overlying the optic thalamus, the animals hemorrhaged heavily: every time I managed to stop the hemorrhage with pulverized resin, I noticed that after a short while the crows were able to stand up but remained immobile in that same position: if I shook them they moved automatically, and I was able to verify that their sight and hearing was totally lost. In fact, I was unable to confirm the observations made by the celebrated Flourens and Longet that a large amount of sight was spared, such that birds deprived of both brain hemispheres moved their head in the direction of the light that was presented: this I could never verify. In these experiments of removal of the cerebral hemispheres, I had time to observe that some movements are still possible in the animals on which these procedures were done, movements that at first appear to be voluntary, but in fact are not: when I opened the beak of one of these and introduced a piece of meat I saw it shaking its head as if it wanted to remove the meat from its mouth. By close observation I was able to determine that this movement was caused by the reflex action of the respiratory nerves, since this does not happen if the piece of meat introduced into the mouth does not come to rest against the internal aperture of the nostrils or the airway aperture, thus blocking the free intake of air for respiration.
In other experiments I blinded one eye of various baby chickens or ducks just born or a few days after birth. I kept them alive for many months, some even 1 year, and found that in all of them the optic nerve was atrophied, more or less ash-colored and gelatinous; a state also present in the square aja22 that divided into two ash-colored fascia hugging the opposite nerve; in this manner the right nerve passes in between [the] left one; and if I follow this ash-colored fascia over the square aja it seems the crossing was total. In others I observed that the part that was most atrophied was the optic lobe, of which the surface was completely ash-colored: in any case I saw only a small reduction of the optic lobe while the optic thalamus and the rest of the nerve were reduced quite a bit. With respect to the good eye, the corresponding optic lobe was well developed but the rest of the nerve was not; but there were no cases in which I found very enlarged the section of the nerve between the thalamus and the eye, and nothing in the optic lobe. From all these anomalies, we can infer the various connections the aforementioned nerve has with the abo
ve-mentioned encephalon, relations that are in harmony with anatomical and physiological observations.
In mammals the relationship of the optic nerve with parts of the brain are more or less the same. The origins of the nerve are from the bigeminal eminence, especially the nates23 [superior colliculi], optic thalamus and its appendices: the medullary fascia coming from the circumvolutions of the posterior part of the cerebral hemisphere, some fibers from the cerebral peduncles, from the lateral walls of the infundibulum of the third ventricle, and from the tuber cinereum. These relationships are the same in the rabbit, ox, lamb, horse, dog, and human: in the horse more than any other animal it has been demonstrated how much the optic thalamus is the same, and how its fibrous fascia, that exit and form the optic nerve, follow the fibrous fascia that exit from the external side of the same thalamus, that go on to then form the fibrous apparatus of the cerebral superior and posterior inferior circumvolutions.
Although from these anatomical data we can conclude that the above-mentioned cerebral parts with which the optic nerves are in relation must affect the integrity of the function of the nerve, I wished to also conduct experiments with live sections. In conducting these experiments I took precaution while damaging one or the other part of the brain, to make as little damage as possible to the other objects. Therefore, making a very small circle of holes, I trephined the skull of rabbits and especially dogs. I introduced a slender pointed knife as wide as a line,24 and cut transversely one-fifth of the anterior part of the brain hemispheres. The animal, let alone, walked and ran as if nothing had hurt it: its muscular energy and its intellectual faculties did not appear diminished, but the sight of the opposite eye was damaged. In other animals, cutting transversely the thickness of the corpus striatum, I noted always loss of sight from the opposite eye and nothing more. In some, when the anterior part of the optic thalamus was cut, the opposite eye was blind without the animal suffering any other damage. Finally, in a dog, I uncovered one section of the brain, very much below the parietal hump, and removed a small portion of substance: nothing happened, except blindness in the opposite eye. The same operation conducted simultaneously in both cerebral hemispheres resulted in complete blindness. These experiments replicated several times prove to me that truly the parts of the brain that are in anatomical relation with the nerve important for sight exercise an important influence over them.
To further confirm my assumption I will succinctly explain the pathological facts observed in rabbits, dogs, ox, horses, and donkeys.
In several rabbits just a few days old I removed the corner of the left eye, emptying it thus of its humor. After 1 year we checked the resulting effects. The left eye, and also the orbit (Table IX [here shown in figure 9.2], Figure 1), were atrophied, while the right eye and orbit were overdeveloped. Exposing the skull, the posterior and superior part of the left side was more protruding, and this I also observed in the corresponding cerebral hemisphere. I also found a significant difference between the two optic nerves; the left was reduced and very slender, the right was quite well developed in the back of the square aja (Table IX, Figure 2) and circled the cerebral peduncle and flattening out it enlarged over the left optic thalamus, over the geniculate eminences and on the superior surface of quadrigeminal eminence (Table IX, Figure 1e–h)
Blinding one eye in several pre-weaned dogs, and 1 year later observing the superior part of the skull opposite to the good eye 1 year later, revealed a greater rise (Table IX, Figure 3a), a rise that is also observed in the corresponding cerebral hemisphere. Cutting the cerebral hemispheres at the level of the corpus callosum, and removing them in order to reveal the vault with three columns, I saw its margin, that was ugly, very large, and rounded, such that one might consider it the continuation of Ammon’s Horn, more elevated along the left side than on the right; by also removing the vault, I realized that this difference depended on the major development of the objects contained in the left lateral ventricle compared with that on the right. Between these objects the more enlarged were clearly the optic thalamus with its geniculate body, and the corpus striatum (Table IX, Figures 4a–c). Between the superior quadrigeminal eminence there did not exist great diversity; between the inferior ones though the left was more developed
Figure 9.2
Panizza’s Table IX. Figure 1. Brain of a rabbit that was blinded in the left eye when young. The corpus striatum, optic thalamus, and the left quadrigeminal eminence corresponding to the right eye are more developed (e–h). Vice versa for the opposite side (a–d). Figure 2. Inferior region of the same brain that shows the atrophy of one nerve relative to the other (a–d). Figure 3. Skull of a dog blinded in the left eye before it was weaned. After 1 year the skull showed an increase on the left side (a). Figure 4. Objects of the brain cavity of the above dog. We can see that the corpus striatum, optic thalamus, the geniculate body and the bigeminal eminence on the left are more pronounced, particularly the external contour of the posterior part of the optic thalamus: (a) corpus striatum, (b) optic thalamus, and (c) geniculate body. Figure 5. Inferior surface of the same brain, where you can see the difference in volume of the two nerves before and after the aja (a–d). Figure 6. Section of the brain of a horse that had lost the right eye many years earlier. The right optic nerve has atrophied, while the left is highly developed. In the objects in the ventricle the right optic thalamus was more developed and protruding in the rear (b), just as are the corresponding bigeminal eminence (c). Figure 7. Inferior surface of the same brain where you can see the great difference in volume between the two nerves (a–d), and how the geniculate body is pronounced (e). Figure 8. Section of a calf brain that was blinded in the left eye after an injury a few days after birth. Killed after 5 months, the left olfactory and optic thalamus were developed, as were the corresponding bigeminal eminence (a–d), while the opposite parts were atrophied. Figure 9. Differences between the two nerves (a–d) before and after the square aja of the above calf. Figure 10. Brain of the C. viridiflavus that serves to demonstrate that the two optic nerves at meeting in the aja form a fissure, where one passes in the other without mixing. Figure 11. Section of the chameleon brain that shows that each optic nerve when it meets the other divides into three fascia that within the fissure intertwine with the fascia of the other without mixing. They intertwine like the fingers of one hand with the other without mixing (a). Figure 12. Brain of a crow showing the decussation of the optic nerves. Figure 13. Brain of a duck showing the perfect decussation of the optic nerve. Figure 14. Decussation of the optic nerves in a chicken. Figure 15. Superior surface of the square aja of humans. Figure 16. Square aja shown from its inferior surface.
Dissecting the brain of horses blinded in one eye, I was able to make various observations, one that enabled me to draw Figures 6 and 7 of Table IX. The brain was that of a horse blinded in the right eye: this optic nerve was very slender, ash-colored, gelatinous, whereas the other was large and very white. On the superior surface of the square aja you could see a small portion of the atrophied nerve running diagonally from the nerve coming from the other side and immersing itself like a wedge in its substance to exit from the opposite side. In the inferior surface of the aja at the join you could see a white streak that crosses diagonally, and similarly directed itself to the opposite side. On the superior surface of the aja we could see many fibers that originated from the tuber cinereum and extended directly from the posterior margin of the chiasm to the anterior margin where they partly inserted themselves into the atrophied nerve. Behind the chiasm one could see the ash-colored left optic nerve up to the thalamus, and its volume was greater than that of the nerve that was located to the right in front of the aja. There was also a difference in size between the two thalami; the right one was better developed, as was the inferior geniculate body and the right quadrigeminal eminence (Table IX, Figures 6a–c and 7c–e), as well as [the] lateral medullary column of the right peduncle of the brain and the external fibrous apparatus of the optic thalamus that extends to the posteri
or superior circumvolutions.
With respect to humans, I refer only to the case of the cadaver of a young girl of 18 years that at the age of 3 years, from a stone hitting her left eye, had lost sight in her eye because it had become atrophied. The skull associated with the right parietal lobe showed a clear depression along the occipital margin of the bone. The corresponding cerebral mass was also depressed. On dissection of the brain, it was found that the left corpus striatum was swelled along its whole body when compared with the right one, thus from the point of its major elevation it was distant two lines from the septum lucidum, the other one, on the other hand, that is, the left one, was only half a line away. This was even more clear: the left optic thalamus was also more developed; there was almost no difference in the quadrigeminal eminence. In the dissection of the objects of the ventricles we found greater consistency in the left ones. Of the optic nerves, the left one, from the eye to the chiasm, was ash-colored and atrophied; behind the aja, the right one was smaller than the left one, but was not of a different color.
To confirm how much the integrity of the optic thalamus and of the corpus striatum influences the organs of sight, I refer to two important facts that I uncovered. A human with a hot temperament, 60 years old, one day while eating had a fainting episode from which he recovered quickly and was able to categorically answer questions presented to him: the entire right part of the body was in a state of paralysis with respect to both senses and motion: the pupil of the right eye was dilated and immobile, and the sight was almost all lost. Placed in bed, and despite attention and care, the morbid symptoms continued to worsen, his intelligence continued to decrease, after 12 [hours] the sick human was completely apoplectic with complete paralysis of sense and motion on the right side of his body; he died on the fourth day. As soon as the problem began, having noticed blindness of the right eye, I predicted that the hemorrhage had to be located in the left optic thalamus. In the dissection we could find almost no infection of the meninges, and of the surface of the brain, little fluid in the ventricles, and instead a lot of blood was in the thickness of the left thalamus.
A Hole in the Head Page 17