406 SCHULTE, SEI WHALE. 



and ventral divisions. In the neck and intermandibular regions the nerve supply is derived 

 from several branches of the facial which have a general ventro-rostral direction on the deep 

 surface of the muscle. One of larger size emerging at the anterior border of the depressor man- 

 dibula? crosses the masseter and is continued rostrad parallel to the lower margin of the mandible 

 in a position which might lead to its confusion with the mylohyoid nerve. 



This description of the panniculus differs materially from the observations of Carte and 

 MacAlister upon a specimen of Balcenoptera acuto-rostrata. They report a platysma myoides 

 which "could be seen only in the median line," and found that the "portion of the neck external 

 to the inner margin of the sternomastoid had no superficial muscular investment." On the 

 other hand Stannius : describes in Phoccena a panniculus with dorsal and ventral divisions sepa- 

 rated by a lateral raphe and except in the intermandibular region and in its more intimate rela- 

 tions to the pectoralis closely resembling the superficial musculature of this foetus of B. borealis. 

 A panniculus of the Phoccena type is also present in foetuses of Tursiops truncatus, and Murie 2 

 has described one of extensive but modified development in Globiocephalus. The conclusion 

 would therefore seem warranted that the panniculus is extensive and highly developed in the 

 Cetacea (Leche), 3 and that Balcenoptera is not an exception to the rule, but in correlation with 

 its throat furrows possess this muscle in a highly developed form. The persistence of the sub- 

 cutaneous musculature in these well-nigh hairless forms can not wholly be ascribed to its inser- 

 tion upon the flipper, but would seem to stand in relation to the maintenance of pressure upon 

 the contents of the abdominal and thoracic cavities as the animal rises to the surface; in accord 

 with this view is the confinement of muscular fasciculi to the ventral and lateral regions of the 

 trunk and their replacement by aponeurosis over the massive dorsal muscles and upon the 

 pedicle. 



Cavum ventrale. This is an extensive area of very delicate areolar tissue which gives way 

 almost without dissection. It reaches from the intermandibular region to within a short dis- 

 tance of the umbilicus. Ventrally it is closed by the muscle complex of the ventral pouch, 

 which is reinforced on the side turned towards the cavum by a strong and moderately thick 

 aponeurosis. At the sides its boundaries are formed by the sternomandibularis and their invest- 

 ing fascia. The dorsal limit is given by a dense and thick aponeurosis which covers the supra- 

 and infrahyoid muscles and from its position corresponds to the usual deep fascia of the neck. 

 Over the pectoralis and external oblique it becomes thinner, and as it approaches the umbilicus 

 it fuses with the aponeurosis of the pouch muscles and so closes the cavum caudally. Rostrad 

 the space does not extend quite to the symphysis and bodies of the mandibles, but is brought to 

 an end inside their arch by the approximation of the pouch muscles to the genioglossus. 



The musculature of the ventral pouch. In addition to the panniculus this comprises the 

 mylohyoid and a longitudinal stratum of cervico-hypoglossal innervation. The muscles are 

 in the form of thin sheets very firmly united by connective tissue. Their general arrangement 

 in cross section is shown in the accompanying photomicrograph (Text-fig. 4). Ectally are 

 scattered bundles of the dorsal panniculus, obviously here equivalent to the platysma myoides. 

 These are followed by the more abundant fasciculi of the ventral division, cut nearly at right 

 angles. The mylohyoid forms the third layer and is very tenuous. Entally are the larger 

 bundles of the longitudinal layer which is thicker than any of the others. 



1 Beschreibung der Muskeln des Ttimmlers (Delphinus phoccena). Miiller's Arch., Jahrg. 1849. 



2 On the Organization of the Caaing Whale, Globiocephalus melas. Trans. Zool. Soc. London, Vol. VIII, 1874. 



3 Braun's Klassen und Ordungen des Thier-Reichs; Saugethiere, Bd. I, p. 669. 



