NERVOUS SYSTEM. VERTEBRATA. .1J:', 



D. 761. Parts of the cranium and neck of ;i jrooag < Y..e,Mlil' with 

 the brain and cervical part of the spinal cord e\jn 

 above. The cord is surrounded by two protective mem- 

 branes the dura mater which has been divided along the 

 dorsal mid-line and turned to either side, and a delicate phi 

 mater closely investing the cord and earning tin- hl.M.d- 

 vessels. Between the two sheaths is a subdural Ivmpli- 

 space. The arteries of the pia mater have been inj 

 The entrance of the dorsal roots of the spinal nerves into the 

 cord by several spreading rootlets is clearly seen through 

 the transparent pia mater. The brain has been preserved 

 to show its comparatively small size in relation to the 

 spinal cord. The right tympanic membrane and columdla 

 auris are also shown. 0. C. 1348. Hunterian. 



D. 762. The hinder part of the spinal cord of a young Crocodile, 

 isolated. This is apparently the rest of the cord shown 

 in the preceding specimen. It has been cut off at the 

 anterior end of the brachial enlargement (the posterior 

 limit of the previous specimen) and its arteries have been 

 injected. The brachial and crural enlargements are of 

 moderate development. Behind the latter, the cord rapidly 

 diminishes to form the caudal segment. The extreme caudal 

 end has been removed. The cord is enveloped by the pin 

 mater, and in places also by the dura. 0. C. 1349. 



Hunterian. 



D. 763. The brain and spinal cord of a Tortoise (Tettudo gr< 



This specimen is a striking example of the correlation that 

 occurs between the size of the different regions of the central 

 nervous system and the activity of the parts innervated by 

 them. In the Tortoises movements are mainly restricted to 

 the head, neck, tail, and limbs, the trunk region Iwin^ 

 rendered immotile by the development of the carapace. 

 In consequence of the absence of the greater part of tin- 

 usual muscles and integumentary sense-organs from thi- 

 immotile region, the cord and spinal nerves arc here re- 

 markably slender. In its other parts (cervical and caudal 

 regions and limb swellings) the cord shows a considerable 

 state of development. 



