PAPERS ON BIOLOGY AND AGRICULTURE 119 



gion to join a peculiar structure, the fused bulla of the 

 other pair of temporal bones (Fig. 10, fab). The skull is 

 understood to be a fused structure, as will appear in the 

 discussion on the skeleton; and thus it would follow that 

 the normal bulla are but opposites of the adjacent heads, 

 and that the related hyoids, although apparently normal 

 on the ventral larynx, must be of independent origin 

 (Fig. 6). 



The oesophagus joins the dorsal wall of the ventral 

 larynx, so that the ventral tracheae and oesophagus are 

 confluent here. A single opening, the glottis, connects 

 this region with the unpaired pharynx above. Likewise 

 a glottis is present on the dorsal larynx, and associated 

 with it is a normal epiglottis, a similar one existing in 

 connection with the ventral larynx above described. 



THE XERVOUS SYSTEM 



Two spinal cords are present, enclosed within separate 

 neural canals. Posteriorly, that of the small pig reaches 

 only to the sacrum, where it abruptly terminates; while 

 that of the larger pig is more normal, terminating in a 

 typical cauda equina. Lumbar and cervical swellings are 

 present as well as normal spinal nerves. 



Anteriorly, each cord passes forward through a fora- 

 men magnum on the posterior angle of the fused cranium, 

 and then each joins its mate to form a partly fused encep- 

 halon. Myelencephalon and metencephalon are indepen- 

 dent of each other and are joined to their respective 

 cords ; but the superior colliculi of the mesencephala re- 

 present the most posterior point of fusion of these parts, 

 for here a firm junction is established and fiber tracts 

 cross as in a chiasma. 



Just posterior to these fused superior colliculi and in 

 the region between the hind brains is a compound ner- 

 vous structure, evidently formed by the fusion of the 

 left optic stalk of the right encephalon with the right 

 optic stalk of the left encephalon. This peculiar struc- 

 ture continues posteriorly and dorsally from the normal 

 position of the optic chiasma, and terminates in connec- 

 tion with the small amorphous structure on the median 

 dorsal line of the skull just anterior to the fused exter- 



