NECTURUS 15 



not readily distinguished from above.) IX-X. Four roots one 

 after the other form the next nerve. The most anterior of these 

 is the glossopharyngeal nerve, the rest compose the vagus nerve. 

 All unite to form the vagus ganglion, from which several nerves 

 can be traced. 



Remove the brain from the skull and draw its ventral surface. 

 Note the origin of the optic nerves (they really cross) and the 

 large hypophysis, a structure in the median line between the floor 

 of the 'twixt-brain (infundibulum) and the medulla oblongata. 

 The roots of the sixth nerve (abducens) may be found near the 

 middle line of the lower surface of the medulla nearly between 

 the roots of the glossopharyngeal. 



SKELETON 



The skeleton consists of axial and appendicular portions. 

 The axial skeleton includes the vertebral column, ribs, and skull; 

 the appendicular consists of the framework of the limbs and the 

 arches or girdles by which they are connected to the trunk. The 

 vertebral column may be divided into four regions: cervical 

 (neck), dorsal (trunk), sacral (articulation of girdle of hind limbs), 

 and caudal (tail). 



Study a vertebra from about the middle of the dorsal region, 

 making out the following features. On the ventral side in the 

 middle line a body or centrum shaped like an hour-glass. Is it 

 concave in front (procoelous), behind (opisthoccelous) , or at both 

 ends (amphicoelous) ? Dorsal to the centrum is the neural arch 

 enclosing a spinal canal for the spinal cord. This arch consists 

 of two plates (neurapophyses) which meet above and bears on its 

 dorsal surface a projection, the neural spine. 



In front each neurapophysis bears a projection, the prezyga- 

 pophysis, which articulates with a similar postzygapophysis 

 developed from the vertebra in front. How do these zygapophyses 

 overlap? 



Extending laterally from each vertebra is a transverse process, 

 directed outwards and backwards and composed of two parts, 

 a diapophysis, arising from the neural arch, and a parapophysis, 

 from the centrum. Dia- and parapophyses are connected by a 

 thin plate, the vertical lamina, and the parapophysis is expanded 

 at its base by a similar horizontal lamina which unites with the 



