138 THE STKUCTURE OF MAN 



form and size are evident to the naked eye, and are, I consider, 

 to be interpreted as progressive. This is the lobus occipitalis 

 of the cerebral hemisphere, in which we find great variation 

 in the extent of the calcar avis, and the posterior cornu of 

 the lateral ventricle. Exact statistics on this subject are a 

 desideratum. 



[In connection with the question of structural degeneration of the brain, 

 certain recent observations of Forsyth-Major are of especial interest. It has 

 been generally assumed that the smooth cerebrum and exposed cerebellum of 

 the Lemurs, which are placed at the root of the order Primates of which Man 

 is the highest member, are primitive characters, indicative of a relationship 

 with and origin from a lowly order of Mammals. Forsyth-Major has discovered 

 evidence of structural simplification and degeneration, during Ontogeny, of 

 the brain of certain Lemurs (apparently in correlation with preponderating 

 development of the face and nose) which points to the conclusion that the 

 supposed primitive characters named may be secondary and retrogressive 

 a welcome suggestion, in view of Cope's discovery that the oldest known 

 Lemurs (Anaptomorphidae) had large and highly - organised brains. The 

 brain of the human foetus, at from three to five months, develops certain 

 convolutions which are early lost and have nothing to do with those of the adult. 

 Kolliker, Beer, Cunningham, and others have investigated them, and the 

 latter, suggesting that they may be the expression of mechanical effects conse- 

 quent on a " quadrupedal growth pause " in development, has proposed to 

 term them " transitory fissures " (microgyri of Beer). Considerable interest 

 attaches to the occasional appearance of convolutions upon the surface of the 

 hemispheres in normally smooth-brained Mammals ; as also to the question 

 whether these are progressive structures, or conversely, whether they, and 

 the convolutions which seem to disappear during Ontogeny among the 

 Lemuroidea, may have anything to do with the "transitory fissures" above- 

 named. A wide field of inquiry is here opened up, which gives promise 

 of most important results.] l 



PERIPHERAL NERVOUS SYSTEM 



But few retrogressive phenomena are here met with ; among 

 these are the present condition of the rami recurrentes of the three 

 branches of the trigeminus and of the vagus, which run to the 

 dura mater, and further, of the ramus auricularis of the latter nerve. 



The fact that in the region of the hypoglossus vestiges of 

 the posterior roots with their ganglia have been found in human 

 embryos, as they were long since in certain lower Mammals, 

 indicates that assimilation of spinal or vertebral elements may 

 be going on in the occipital region of the skull. Certain delicate 

 nerve loops which lie in the region of the trigeminus, facialis 



1 [Cf. Forsyth-Major in Rothschild's Novitates Zoological, vol. i. p. 35 ; and Cun- 

 ningham, Cunningham Memoirs, E. Irish Acad., No. VII. p. 30.] 



