96 bulletin: museum of comparative zoology. 



dissections indicated a connection with the median sympathetic 

 trunk, the study of sections shows this to be only a connective-tissue 

 union, the sympathetic bundle passing directly across without any 

 break in its sheath that would indicate the passage of nerve fibers. 



V. GENERAL CONSIDERATIONS ON NERVE XII AND 

 THE SPINAL NERVES. 



From a comparative standpoint the hypoglossal nerve in Anolis 

 presents two questions for consideration: First, as to the number of 

 spinal nerves that enter into its formation and their position in the 

 series of spino-occipital nerves, and, secondly, as to the differentiation 

 of its component neurons from the typical somatic-motor type from 

 which they come. The first question appears to be answered in part 

 by the obvious facts presented by Anolis itself, through the persistence 

 of three distinct occipital foramina, indicating three separate seg- 

 mental nerves. Only rarely have three cranial roots for XII been 

 described in the adult saurian. Among all those described by Fischer 

 ('52, p. 66), three roots are mentioned for only Platydactylus; but 

 in Anolis not only are there three roots, but they emerge through 

 separate foramina. In two species he finds only one root, and in 

 seven he finds two. In all cases XII either unites with the first spinal 

 or receives branches from it. Fischer states that, as a rule, the first 

 two spinal nerves are without dorsal roots and ganglia, although some- 

 times there occurs a weak dorsal root on the second spinal nerve. As 

 in Anolis, the third is a nerve well developed in both its motor and 

 sensory components. The relation of XII to the spinal nerves varies 

 according to the strength and number of its roots. This fact points 

 to the correctness of Fischer's view that the cranial part of XII does 

 not represent the same number of spinal nerves in all lizards. Fiir- 

 bringer ('97, p. 501) arrives at the constant number of three roots for 

 all sauropsida, although the first and second emerge through a common 

 foramen in most reptiles. Reference to Fiirbringer's table (p. 546) 

 shows his conclusion regarding the homologies of these nerves. He 

 designates them, the first three, as occipito-spinal nerves, their position 

 being fixed through discovery in the embryo of the older occipital 

 nerves (anterior to these), which have a transitory existence. There 

 are two features in the twelfth nerve of Anolis which seem to show 

 that it is less completely incorporated into the head than in other rep- 



