410 SCHULTE, SEI WHALE. 



dorsal gain an insertion into the postglenoid process of the squamosal and the fibrous struc- 

 tures adjacent to the temporo-maxillary articulation. The deeper stratum has interesting 

 relations. Its dorsal fasciculi terminate in an intermuscular septum which attaches them to 

 the posterior belly of the digastric in almost its whole length. Its ventral fasciculi which appar- 

 ently are separated from the rest of the muscle by a tendinous inscription (this is clearly present 

 in Megaptera) and are distinguished as well by a more longitudinal course are divided into two 

 slips. The dorsal of small size, applied to the lateral surface of the posterior belly of the digastric 

 and united to it by a common septum passes horizontally forward to be inserted into the body 

 of the mandible below the attachment of the masseter. This slip thus arises from fibrous inscrip- 

 tions, which unite it with both the sterno-mandibularis and the depressor mandibulse (posterior 

 belly of the digastric). It is of larger size and of better definition in a foetus of Megaptera longi- 

 mana and there I was able to demonstrate its innervation from the mylohyoid branch of the 

 fifth. It is therefore to be interpreted as the anterior belly of the digastric. The remaining 

 slip, of considerably larger size in Balcenoptera, is directed rostrad parallel to the foregoing and, 

 in part overlapping it, is lost in the dense fibrous tissue between the mylohyoid and panniculus. 

 This slip was small in Megaptera. In both foetuses it was innervated by a branch of the seventh 

 nerve. In both forms there was a general correspondence in the make up of this muscle com- 

 plex, and I have relied upon the data obtained from the Megaptera foetus for confirmation of the 

 findings in the smaller and in this region less well preserved Balcenoptera. The chief differences 

 in the arrangement in the two forms lies in the development of a muscle-free interval in Megap- 

 tera between the mandibular and postglenoid divisions of the muscle. Here a triangular apo- 

 neurosis is present and is continued superficial to the anterior belly of the digastric and the 

 facialis slip. I am quite sure that muscle fasciculi were present in this position in B. borealis, 

 though infiltrated with fat, the precise distribution of which I could not determine. It would 

 seem therefore that the mandibular insertion in Megaptera defaults, the superficial stratum here 

 being replaced by fascia. The muscle would seem therefore to consist essentially of fasciculi 

 of thoracic and mesal origin directed to the mandible and the region adjacent to the temporo- 

 maxillary articulation. This system of fasciculi is innervated by the hypoglossal after its com- 

 munication with the cervical nerves, several small branches entering at the lateral border of 

 the sterno-hyoid and others being derived from the large division of that nerve which runs over 

 its ental surface. To this, on its deep surface, slips of quintal and facial innervation have 

 gained attachment; the former attached also to the depressor mandibulse constitutes the ante- 

 rior belly of the digastric. 



Muscles of mastication. The masseter is composed of two layers which are completely 

 separate, the superficial small, triangular and very oblique in position, the deep quadrilateral, 

 of large size and intersecting the superficial portion, by which it is deeply grooved, almost at 

 right angles. In recognizing but two layers I am in agreement with Carte and MacAlister; 

 the middle division of Beauregard's l careful description of B. musculus seems here to form an 

 intrinsic part of the deep stratum. The superficial portion. arises by a small flattened tendon 

 from the orbital aponeurosis, just mesal to the zygoma at the junction of its middle and caudal 

 thirds. Here it is continuous with strong band-like thickenings of the aponeurosis, which col- 

 lectively form a sagittal arch of tendinous structure and ventral convexity. Its caudal arm is 



1 Beauregard, H. Etude de 1'Articulation temporo-maxillaire chez les Balaenopteres. Jour, de 1'Anat. et de la Phys., An. 18, 

 1882, p. 16. 



