TKAXSAC'l'lONS Ol' THli SECTIONS. 141) 



On a lfi/ihvci:£huHc Skull, and on the Duijlicity of the Tenipoml Kid^e. 

 By Prof. Cleland, F.R.S. 



On the Sjpinal JS'ervom iSi/stcm of ihc Cciacca. Bj/ D. J. CrNxiNcnAM, 3I.D., 

 Senior Dei)ionstrator of Anatonnj, Edinhurgh University. 



At the outset of my invesiigations into the anatomy of the spinal nervous system 

 of the Cetacea, I endeavoured to discover whether any anatomist had described the 

 arrangement of these nerves. This was no easy matter, so little had been written 

 on the subject. H. liapp (' Die Cetaceen,' Stuttgart, 1837) states that, " with respect 

 to the course of the spinal nerves (of the Cetacea) there are no researches ;" and 

 ytannius ('Lehrbnch der Vergleichenden Anatomic,' Zweiten Theil, 18-J(>, p. 393) 

 simply mentions that "in the Dolphin a nerve-trunk proceeds out of the lumbar 

 plexus, the branches of which are intended for the muscles of the rudimentary 

 pelvis, and for the external genital organs aiid their muscles, as well as for the 

 region of the anus." Indeed it was not until I had finislied my investigation that 

 .1 discovered that Swan, in the " Table of Contents " or Introduction to his work 

 upon the ' Comparative Anatomy of the Nervous System,' published in 1835, 

 gives a short account of the whole nervous system of the porpoise. I believe, 

 however, that besides extending liis account very materially, I am able to give 

 additional results ; and I have taken care to have all my dissections illustrated by 

 drawings, whilst he, with his wealth of plates of the nervous system of other ani- 

 mals, does not give one of the nervous system of the Cetacea. 



1 may mention that the following results are derived from the dissection of four 

 members of the Cetacean group, viz. three porpoises and one dolphin*. 



Spinal Cord. — The spinal cord is surrounded and supported on all sides by the 

 d^mse rete mirabile, which may be looked upon as performing a threefold function : 

 (1) it constitutes a soft pliable packing material, by means of whicli tlie cord is 

 protected from shocks ; (2) it maintains a uniform warmth around this important 

 and delicate nervous centre by keeping it constantlj' bathed, as it were, in warm 

 arterial blood ; (3) and lastly, as Professor Turner has pointed out (Trans. Roy. 

 Soc. Edinb. vol. xxvi. p. 233), it subdivides the arterial stream^ and equalizes its 

 force before it reaches the brain and spinal cord. 



In the porpoise the spinal cord extends from the margin of the foramen magnum 

 to a point corresponding to the interval betw^-en the 6th and 7th lumbo-caudal 

 vertebra^, and opposite to the foramina of exit of the 27th pair of spinal nerves. It 

 presents two enlargements — one in the cervical, and the other iu the lumbar region. 

 The former of these is connected v,ith the nerves which go to form the cervical and 

 brachial plexuses, and the latter with the nerves which supply the genital organs 

 and the muscular apparatus of the tail. Between these enlargements the cord is 

 of uniform diameter, and the lumbar swelling tapers away in a fusiform manner 

 into the filum terminale. 



Boots of the Spinal Nerves. — The direction and length of the nerve-roots and the 

 size and position of the ganglia vary in the dift'erent regions of the spine. 



The nerve-roots which proceed from the cervical and luiubar enlargements of 

 the cord are closely crowded togetlier, whilst iu the dorsal region they are placed 

 at considerable intervals from each other. Those arising from the lumbar swelling 

 are very long, tortuous, or curly, loosely bound together by lax connective tissue, 

 and they constitute the cauda equina. Tliey pass directly backwards to reach 

 their respective foramina of exit. The dorsal and cervical nerve-roots are much 

 shorter, and the former are directed outwards and backwards, whilst the latter, 

 with the exception of the first three which pass directly outwards, take a course 

 outwards and forwards. 



In all the regions the superior nerve-roots are smaller than the inferior — thus 

 constituting a marked contrast to most mammals, in which tlie reverse of this 

 arrangement holds good. Nowhere, however, is this diti'erence in size so marked 

 as in the cauda equina, iu the last nerves of which the superior root is half the size 



* A yoimg specimen of D. albirostris {vide Proc. Zool. Soc. 1876, p. 679). 



