150 DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 
represented by a short but fairly developed mass of muscle and fibroid tissue, which 
covers the anterior inferior blunt point of the mandible and mingles with the submucous 
tissue of the lower lip. 
Laterally, covering the outside of the swollen symphysis, and reaching the concavity 
of the horizontal ramus, is the depressor labii inferioris, a broad, fleshy, and most 
unusually developed plane of muscle. From its inferior attachment the fibres incline 
upwards and forwards, and intermix with the submucous tissues of the mouth and 
under lip. The two muscles of opposite sides traverse round the downwardly pro- 
jecting symphysis and unite behind; but in front of this union there intervenes a 
strongish connecting fascia. 
The homologue of the depressor anguli oris is a thick cap of muscle which projects 
on the lateral and anterior surface of the symphysial knee and overspreads the depressor 
labii inferioris. The fibres of the former have quite a different inclination from those 
of the latter, which cross them at a right angle upwards and backwards. The two 
depressors of the angle of the mouth are connected by a wide, strong aponeurotic 
fascia on the under aspect of the bone; and each as it ascends narrows, and is inserted 
by membrane on the side of the lower lip. 
The nerves and vessels emitted from the mental foramina are distributed to this and 
the preceding muscle. They are very numerous and of considerable size. 
In Whales neither of these three lower-lip muscles can be differentiated; the mylo- 
hyoid and fibres of panniculus cover the rami. The moveable lower lip of the Elephant 
partially derives its power from an extension forwards of the platysmal (facien and 
cervico-facien of Cuvier!) panniculus; but there is besides a broad and fleshy combined 
elevator and depressor of the inferior lip’. 
There is not much difficulty in recognizing the homologue of the orbicularis oris, 
which, as usual, surrounds the oral fissure. Its fibres are in intimate union with the 
anterior part of the buccinator and that portion of the fleshy panniculus or platysma 
which covers the cheeks. 
It is merely represented by a few indefinite fibres in Cetacea; but is a broad band in 
the Elephant (/. c. pl. 274. 1), chiefly arching to the upper lip. 
The dbuccinator (Bu) is large, long, and very thick. Its line of attachment above is 
the beak-like process of the maxillary and intermaxillary bones; and below the eye it 
fills the great vacuity overarched by the projecting orbit. It comports itself to the deep 
bay formed by the ascending ramus of the mandible, and thence proceeds forwards, by 
a broad attachment, to near the front of the upper lip. Single, thick, and fleshy in 
Globiocephalus, wider flat fibres in Elephas as in Manatus. 
Upon the surface of the buccinator, but inferiorly, there lies a long, ribband-like, but 
comparatively thick and completely fleshy slip of muscle, which has origin from the 
fossa on the anterior and inner portion of the ascending ramus. The muscle in question 
' Myologie, plate 272, 2. * Op, cit. pl. 274, n. 
