212 DR. R. W. SHUFELDT ON [Apr. 1, 



The cerebellum is cup-shaped, smooth, and comparatively of large 

 size ; its anterior concavity entirely covers the hinder portion of the 

 optic lobes. Behind it, the dorsal aspect of the medulla oblongata 

 is much scooped out, while its ventral flexure is but fairly well-marked. 



Upon carefully examining the roots of the cranial nerves, the fora- 

 men of Monro, the posterior commissure, the encephalic ventricles, 

 and other minor structures of the brain-mass, I find nothing that 

 might in any way be considered worthy of special record. 



1 will say here, however, that I felt a strong desire to work out 

 the cranial nerves ; they looked very tempting, but my material 

 would hardly admit of it, as my dissections of the eye, ear, tongue, 

 and muscles of tiie head had already made extensive inroads upon tliis 

 part of the bodies of my several specimens, and in consequence the 

 cranial nerves had to be frequently cut or broken up. 



Of the Sacral and Brachial Plexuses. — Coming to the spinal nerves, 

 the only ones to which we have paid any special attention in our subject 

 are the branches that go to make up the brachial and sacral plexuses. 

 These I observed quite closely. But upon studying the descriptions 

 and examining the figures of these parts in a goodly number of species 

 and genera of reptiles as given us by a great many anatomists, I have 

 been forced to believe that these structures will never be anything 

 more than uncertain ones in so far as they afford any reliable cha- 

 racters for classificatory purposes. Mivart speaks to the ])oint in 

 reference to this matter when he says, " As to the particular spinal 

 nerves which go to form these plexuses respectively, and as to the 

 mode of their interlacement and mode of giving origin to the limb- 

 nerves, there is not only diversity between different genera of the same 

 order and s|)ecies of the sanie genus, but also between different 

 individuals of the same genus, and even between the two sides of the 

 same individual reptile" \ 



Regarding the brachial plexus in an adult specimen of Heloderma 

 before me of the right side, I find that the fifth nerve that emerges 

 from the spinal column, in addition to its sending off its smaller 

 branches for muscular supply in its vicinity, also sends a long delicate 

 branch which merges with the sixtii spinal nerve, and so it constitutes 

 the anterior part of the brachial plexus. The sixth, seventh, and 

 eighth spinal nerves are very considerably larger than any of those 

 that precede them or that immediately follow them, and they may be 

 considered as constituting the main portion of the plexus. As they 

 come out of the intervertebral foramina of the spine, the first two 

 mentioned nerves pass over the posterior end of the rectus anticus 

 major muscle, while the eighth spinalis still more extensively covered 

 by the most anterior fasciculus of the retrahentes costarum series. 

 Now the sixth spinal nerve as it approaches the shoulder-joint gives 

 off four princi[)al branches whicli supply various muscles of this 

 region, and a little further on at its termination this is the fate of 

 the main trunk itself. It, however, also sends off a short and rather 

 thick branch that joins and merges with the trunk of the seventh 

 nerve, before the latter anastomoses with the eighth. Following out- 

 ' Enoyclopa?dia Britauuica, Otli edition, article " Eeptiles,'' vol. xx. p. 400. 

 [fifi] 



