DISSECTION OF THE DOG 221 



An indistinct narrow ridge of fibres winds round the cerebral peduncle 

 beginning at the brachium of the anterior colliculus and ending vaguely about 

 the mammillary body. This is the transverse peduncular fasciculus (fasciculus 

 peduncularis transversus [Guddeni]). 



Dissection. — Cut across the mid-brain, making the section through the 

 anterior colliculus but not so far forwards as to injure the geniculate 

 bodies. 



An examination of the cut surface of the mid-brain reveals the aqueduct 

 of Sylvius, which places the third and fourth ventricles in communication with 

 each other. In general the outline of the aqueduct is lozenge-shaped, and 

 around it is a mass of grey nerve matter. 



The differentiation of the tegmentum and basis pedunculi can readily be 

 made by an observation of the position of the two grooves already noted on 

 the surface. In addition, a stratum of nerve tissue of somewhat different 

 colour lies between the two structures. 



Dissection. — By a median incision separate the two halves of what remains 

 of the cerebrum. Of one half, make a series of horizontal sections about 

 two or three mm. thick. The other half should be cut into slices by 

 vertical transverse incisions. In making these sections it is well to use a 

 broad-bladed knife or a razor. 



Corpus striatum, etc. — The so-called basal ganglia of the cerebral hemi- 

 sphere consist of masses of grey matter separated by intervening strata of 

 white matter. The ganglia are the caudate and lentiform nuclei of the corpus 

 striatum, the claustrum, and the amygdaloid nucleus. 



Nucleus caudatus. — A partial examination of the caudate nucleus was 

 made after the lateral ventricle had been opened. The nucleus consists of a 

 mass of grey matter of curved pear-shaped form. The head (caput nuclei 

 caudati) is thick and forms a projection in the anterior cornu of the ventricle. 

 From the head the nucleus tapers somewhat rapidly to a tail (cauda nuclei 

 caudati), which follows the inferior cornu of the ventricle to end in the amyg- 

 daloid nucleus (nucleus amygdalae) in the roof of the extremity of the cornu. 

 From what has previously been seen and from the sections now under examina- 

 tion, it is manifest that two surfaces of the caudate nucleus may be described. 

 A free ventricular surface is covered by the ependyma of the lateral ventricle. 

 A deeper surface is embedded in the substance of the cerebral hemisphere, and 

 is mainly in contact with the internal capsule. 



Nucleus lentieormis. — The lentiform nucleus is an irregularly lens- 

 shaped mass of grey matter placed lateral to the caudate nucleus and the 

 thalamus. Smaller than the caudate nucleus, it is connected with this by strands 

 of grey matter which cross the intervening white stratum. In addition the 



