306 F. H. EDGEWOIJTH. 



The Anlagen of the superior oblique and external rectus 

 are developed from forward extensions of the upper ends of 

 the mandibular and hyoid myotomes, and the lYth and YIth 

 nerves may be regarded as, phylogenetically, late formations. 



There do not appear to be any investigations on the 

 existence of cell-groups in the Vth motor nucleus, which 

 might correspond to the somatic and splanchnic muscles 

 innervated. The nucleus contains a centre for the anterior 

 digastric, but it is not known whether this migrates, during 

 development, from the facial nucleus, or whether it is locally 

 developed. The fibres of the Yth mesencephalic root join the 

 motor root (Cajal), but it does not appear certain whiit 

 structures it innervates. 



The motor nucleus of the Yllth nerve consists, according 

 to van Gehuchten and Marinesco, of four cell groups, three 

 ventral and one dorsal : of these, the internal ventral is the 

 centre for the stapedius, the middle for the auricular muscles, 

 the external for the inferior facial muscles, and the dorsal 

 nucleus for the superior facial muscles (frontalis, corrugator 

 supercilii, and orbicularis palpebrarum). According to this 

 account there is no special cell-group for the posterior 

 digastric and stylohyoid, which seems unlikely. More 

 recently, Kosaka has stated that the dorsal cell group in the 

 fowl is the motor nucleus for the digastricus. The subject 

 evidently needs further investigation. 



The glosso-pharyngeal nucleus, accoi-ding to v. Gehuchten, 

 consists of a ventral cell-group only ; according to Sti-eeter 

 it has a dorsal nucleus as well as a nucleus ambis'uus. In 

 the monkey (Beevor and Horsley) it innervates the stylo- 

 pharyngeus and (?) the middle constrictor of the pharynx. 

 It is not known whether thei-e is a separate cell-g'roup for the 

 branchio-hyoid it, animals, e. g. pig, dog, where this muscle 

 exists. 



The Xth and Xlth medullary are primitively, in the rabbit, 

 the nerves of the second and third branchia' segments. The 

 Xth efferent fibres arise from dorsal and ventral motor nuclei, 

 those of the Xlth medullary from a dorsal nucleus only (v. 



