THE HORSE. 



179 



' appearance, conoid in form, narrow and approximated 

 inferiorly ; broad superiorly ; they finally contract into 

 medullary bands, the tractus optici, wliich turn round 

 the crura cerebri to the base of the brain. 



Q. How are the thalami distinguished from the 

 corpora striata ? — A. They are more dense and firmer 

 in composition. 



TAENIA. 



Q. What is the situation of the taenia ? — A. They 

 are located in the groove between the thalamus and 

 corpus striatum, partly covered by the plexus choroides. 



COMMISURES. 



Q. Name the commisures of the brain. — A. 1st, 

 commissm'a mollis ; 2d, commism'a inferior cerebri ; 

 3d, commism-a superior cerebri. 



Q. How is the commisura mollis formed ? — A. By 

 contiguous parts of the thalami, which are united by 

 cortical matter. 



Q. How is the commisura inferior cerebri formed ? 

 — By a connection between the hemispheres of the 

 brain. 



Q. Where is the superior commissure located ? — A. 

 Above the commissura mollis ; it has the appearance of 

 a short medullary chord. 



FORAMEN. 

 Q. What is the foramen? — A. It is a triangular 

 depression under the arch of the fornix, into which the 

 lateral ventricles open. 



"STEXTRICLES. 



{^Remarks. — Having put the usual question regarding 

 the lateral ventricles, which may be numbered 1 and 

 2, we now come to the third ventricle, which is not so 

 well marked as in the human subject.] 



THIRD A'ENTRICLE. 



Q. How is the third ventricle formed? — A. By a 

 mere fissm-e existing between the thalami. 



[Remarks. — The fourth ventricle, being located in 

 the cerebellum, will be considered under this head.] 



INFUNDIBULUM. 



Q. Where is the infundibulum located ? — A. At the 

 inferior part of the thii'd ventricle. 



PINEAL GLAND. 



Q. Where is the jjineal gland located ? — A. Be- 

 tween the summits of the thalami, over the third 

 ventricle, and above and before the superior com- 

 missure. 



Q. Describe the jjineal gland. — A. It is a small 

 conoid body, of grayish color, marked by a slight 

 depression along its centre. 



Q. What are its attachments? — A. It is attached 

 • by means of the pia mater to the thalami and tuber- 

 cula quadragemina, 



Q. What is the internal structure of the pineal 

 gland ? — A. It consists of cortical and granular 

 matter. 



NATES AND TESTES. 



Q. Where are the nates and testes situated ? — A. 

 Above the third ventricle, behind the pineal gland, and 

 immediately over and within the third and fourth ven- 

 tricles. 



Q. How do the nates differ from the testes? — A. 

 The former are larger than the latter, and are separated 

 by a groove from the testes, and by a deep perpendicular 

 fissure from each other. 



Q. What is their form ? — A. Semi-oval. 



Q. What is their composition? — A. They are com- 

 posed of cineritous and medullary matter. 



CEREBELLUM. 



Q. What is the situation of the cerebellum ? — A.Jxi 

 the inferior and posterior parts of the cranium. 



Q. How does the cerebellum compare in size with, 

 the cerebrum? — A. The former is only about one- 

 sixth the volume of the latter. 



Q. Describe the appearance of the cerebellum ? — -A. 

 Its surface is lobular and convoluted; its form is 

 irregular, having two oval ends placed transversely, 

 united in the centre by a broad vermiform belt; its 

 lateral dimensions exceed its longitudinal. 



Q. How is the cerebellum divided ? — A. Into three 

 lobes, a central and two lateral. 



Q. How does the composition of the cerebellum 

 differ from that of the cerebrum ? — A. In the former 

 the cortical substance exceeds the medullary, and, 

 instead of forming the bulk of the outer parts, as is 

 the case in the cerebrum, it pervades the inner. 



FOURTH VENTRICLE. 



Q. What is the situation of the fom'th ventricle ? — 

 A. It is situated between the cerebellum, tuber annu- 

 lare, and medulla oblongata. 



Q. Where is the choroid plexus of the cerebellum 

 situated? — A. Within and across the posterior part 

 of the fourth ventricle, between the cerebellum and 

 medulla oblongata. 



Q. How is the choroid plexus of the cerebellum dis- 

 tributed ? — A. It is distributed into three di\-isions : 

 one lies in the middle of the calamus ; the two latter 

 are found witliin fissures in the cerebellum, occupjing 

 the spaces between it and the tuber annulare. 



BASE OF THE BRAIN. 



Q. How is the base or posterior part of the cerebrum 

 divided? — A. It is di\-ided into six lobes. 



Q. Describe their dimions. — A. There are tAvo 

 anterior or inferior, resting upon the wings of the 

 ethmoid bone ; two middle, upon those of the sphenoid; 

 and two superior or posterior, lodged in the fossa of the 

 squamous portions of the temporal bones. 



Q. AVhat name is given to two broad, smooth promi- 

 nences which a^^pear over the middle lobes at the base 

 of the brain ? — A. These are the corpora striata. 



Q. What nerves originate from this vicinity? — A. 

 The olfactorv nen'es. 



