88 bulletin: museum of comparative zoology. 



R. HYPOGLOSSAL NERVE. 



The twelfth cranial nerve is well developed in Anoli.s, in correlation 

 with the condition of the tongue and especially with its muscular 

 tongue papillae. It arises from three distinct roots and, with the 

 exception of the brief union with the pharyngo-laryngeal ramus of IX 

 and X, takes an independent course to the tongue, where the greater 

 part of its fibers are distributed to the intrinsic musculature. A few 

 small bundles are given off to the cerato-mandibularis group as it 

 crosses these muscles. Not all the hypoglossal nerve is distributed 

 to the ventral region, a part of the last (third) root retaining the dorsal 

 and lateral rami of the spinal nerve from which it phylogenetically has 

 arisen. These go to the cervical muscles. 



Roots of the hypoglossal. Although nerve XII is a combination of 

 roots which emerge from the cranium through three separate foramina, 

 there is no separation of root bundles at their origin into three groups. 

 They form a continuous series along the somatic motor line, and a 

 comparison shows that they may be differently combined to emerge 

 from the cranium. There is, however, one feature which is constant, 

 viz., the presence of a cervical part on the last root of the series, which 

 is marked off from the hypoglossal part by a difference in the size of 

 its fibers, thus showing a correlation between its functions (as indi- 

 cated by its distribution) and the structure of its fibers. Special 

 series of sections prepared for the purpose of tracing these differences 

 to central nuclei have thus far failed, owing to the difficulty of carrying 

 them through the meninges of the brain. Where the root bundles 

 pass through the foramina the fibers are well preserved and here the 

 two kinds of fibers are distinctly segregated and were easily followed 

 into their respective rami. 



Distribution of the cervical part (Plates 2, 3, figs. 4-6). The cervi- 

 cal part is made up of larger fibers than those forming the hypo- 

 glossal nerve proper. They equal in caliber the motor components of 

 the first and second spinal nerves, and their distribution is similar. 

 The hypoglossal bundle in the posterior root of XII is in every way 

 like the other roots of this nerve which join it to form the main hypo- 

 glossal trunk. The cervical portion, having a dorsal position in the 

 common root as it emerges from the foramen, divides at once into a 

 lateral {crv. I. XII) and a dorsal {crv. d. XII) ramus. The lateral 

 ramus is the larger and is distributed to the spinalis colli muscle 

 (Plate 7, fig. 23, spi. coll.). The dorsal ramus passes caudad on the 



