SCHULTE, SEI WHALE. 407 



The mylohyoid arises in the usual manner from the oral surface of the mandible along a 

 line which ascends somewhat on the bone in the direction of the ramus. Its fasciculi are directed 

 to the median line with an inclination rostrad to unite with their 

 antimere by means of a poorly developed raphe which permits 

 of some interdigitation, the two halves of the muscle being dis- 

 tinguished more by the inclination of their bundles than by the 

 amount of connective tissue interposed. The innervation is by 

 the usual mylohyoid branches of the inferior maxillary nerve, 

 which also supplies the anterior belly of the digastric and is placed 

 upon the ectal surface of the muscle close to the mandible. 

 There was no attachment either of the raphe or of the mylohyoid 

 to the body of the hyoid, from which the muscle is separated by 

 the longitudinal layer already referred to as the deepest stratum 

 of the pouch. In the post mortem distension of the ventral 

 pouch by gases, the caudal border of the mylohyoid produces a 

 transverse furrow sometimes of considerable depth as is shown * 



in Turner's illustration, 1 and particularly well in Andrews' photo- 

 graph (unpublished). F i g . 4- Photomicrograph of coronal 



The longitudinal muscle of the pouch extends from its caudal secti n of ^ m f c ! es . of the , ventral 



pouch. 1, Dorsal division of panni- 



limit in front of the umbilicus to the mandibular arch. It arises cuius camosus (c/. PI. XLIII, fig. i). 



i ,i i i , r i j 2, Ventral division of same. 3, Mvlo- 



in successive sheets, so that as a whole it is of a laminated struc- hyoid 4> ^^^1 stratum . ' 

 ture, from the deep surface of the intermuscular septum between 



it and the ventral panniculus. The layers of thoracic origin are superficial to those beginning 

 farther caudad. On reaching the mylohyoid it passes upon its dorsal or oral surface and is 

 attached to the mandibles immediately dorsal to the insertion of that muscle. As it approaches 

 the jaw it becomes firmly united with the genioglossus to an extent approximately corresponding 

 to the floor of the alveolingual region, in this detail differing from conditions observed in 

 Megaptera, where it is easily separable from that muscle. The union in Balcenoptera is by con- 

 nective tissue only; I could find no exchange of fasciculi. As the longitudinal layer passes the 

 sternomandibularis in the neck it receives in its lateral portion a contribution of bundles from 

 that muscle, a condition which is more marked in Megaptera. The relation of the two muscles 

 is further shown by their innervation from the hypoglossal after it has received the communica- 

 tion of the cervical nerves, the longitudinal muscle receiving a large branch which ramifies on its 

 ental surface. 



Carte and MacAlister describe a mylohyoid of loose structure, "composed of fine muscular 

 fibres and areolar tissue permeated by numerous blood vessels"; the fibres in the midline inter- 

 lace with those of its fellow; no mention is made of an origin from the body of the hyoid, which 

 as their description is detailed, it may be taken that the muscle did not possess. In the matter 

 of structure, the muscles of this region, though thin, were far more compact in this foetus than 

 in their specimen. As in the fcetus of Megaptera the fasciculi were less coherent and in their 

 interstices delicate areolar tissue was more abundant, it would seem that an increasing invasion 



1 Turner, Wm. An account of the Great Firmer Whale (Balcenoptera Sibaldii) stranded at Longniddry. Part I. The Soft Parts. 

 Trans. Roy. Soc. Edinburgh, Vol. XXVI, 1872, plate v, fig. 1. 



