92 TRANSACTIONS OF THE [jAN. 11, 



ment to the Hyoid served to differentiate the infra-h^'oid from 

 the supra-hyoid division, as in most of the higher mammalia. 

 The evolution of the group indicates cleavage in two planes. 



1. Vertical sagittal cleavage, resulting in the differentiation 

 of Omo-hyoid from Sterno-hyoid, and in the separation, in the 

 median line, of Sterno-hyoid, Sterno-thyroid, Thyro-hyoid and 

 Genio-hyoid from the muscles of the opposite side. 



2. Vertical coronal cleavage, separating Omo-hyoid and Ster- 

 no-hyoid from the subjacent Sterno-th3'roid and Thyro-hyoid. 



The direct continuation of muscles arising from the Sternum 

 into the muscular substance of the tongue is sufficiently marked 

 in the Edentate examples quoted, to warrant the assumption that 

 the intermediate division of the entire group b}' the Hyoid — 

 and to a less important degree in the deeper layer by the Thy- 

 roid — is a secondary character, acquired during the evolution of 

 the mammalian hyoid and laryngeal apparatus, and leading to a 

 further isolation and independent development of the muscular 

 apparatus of the tpngue proper. 



It explains, however, the association in the nerve supply of 

 apparently well differentiated muscular groups, and the connec- 

 tion of the Ansa cervicalis with the motor nerve of the tongue 

 remains in the highest mammalian forms as evidence of the 

 original unity of the hyoid and glossal muscular groups. 



It is only necessary to refer in this connection to tlje results 

 of the researches of Froriep* and Beck,f which demonstrate the 

 morphological position of the Hypoglossus as a compound of 

 several " occipito-spinal " nerves — equivalent to the remaining 

 groups of cervical, dorsal, lumbar, etc., spinal nerves — and prop- 

 perly separated from the category of " cranial nerves." 



The Phrenic nerve in the Cynomorpha arises usually l)y two 

 roots from the Fourth and Fifth Cervical nerves, receiving an 

 additional branch from the combined Fourth and Fifth nerve 

 through the nerve to the Subclavius muscle. 



Fig. IX of Plate VII, represents the nerve in Macacus rhesus. 



It passes down on the Anterior Scalenus, crosses the medial 

 margin of the muscle 2 cm. above first rib, and passes in front 

 and subsequently to the medial side of the Vertebral artery. 

 It descends behind the sternal extremity of the clavicle and first 

 chondro-sternal junction, and at the upper margin of the carti- 

 lage of the first rib receives a communicating branch from the 



*A. Froriep. Ueber ein Ganglion des Hypoglossus und Wirbelanlagen In der 

 Occipital region. Archiv. f. Anat. Ento.. 1882, p. 279. 



A. Froriep and W. Beck. Ueber das Vorkommen dorsaler Hypoglossus wurzeln 

 mit Ganglion in der Reihe der Siiugettiiere. Anat.-Anz. Bd. X., No. 21, p. 688. 



+ W. Beck. Ueber den Austritt des N. Hypoglossus and N. cervicalis primus, etc. 

 Anat. Hefte XVIII., p. 251. (Contains also Bibliography.) 



