140 DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 
in cross diameter. Besides suspensory ligament derived from the transverse process of 
what may be considered a sacral vertebra, there is another, equally strong, passing 
inwards from the pubo-ischial region to the vulva, behind which it meets its fellow 
of the opposite side. This interpelvic bridge appears to be the homologue of a sub- 
pubic ligament. 
4. Cranium and Dentition. 
So often has the skull of the Manatee been described and figured, that I restrict 
myself to a short notice of its interior, and to a few remarks on the foetal cranium. 
The sections chosen to illustrate the cranial cavity are the internal basis as opened 
horizontally or with calvarium removed, and a longitudinal vertical section to the left 
of the middle line. The former (fig. 36, Pl. XXV.), of the female specimen, has the 
dura mater attached on the left side, but the bones have been cleaned on the right; 
the latter (fig. 87, Pl. XXVI.), of the younger male, is part and parcel of the sectional 
view of the body with membranes and organs 7 situ. 
The interior basis cranii may be likened in figure to a broad stirrup, being very square 
across the supraoccipital region, and arching regularly round from the temporal to the 
frontal region. It is flattish below, as is the vault; but the sides of the entire cavity 
are steep and but slightly arched mesially. The length and breadth of the cranial 
cavity are nearly equal; but the height is rather less than either. In the female skull 
(that depicted in fig. 56) the two horizontal diameters were about 34 inches, the vertical 
close upon 2? inches. 
The skull’s walls are very remarkable as regards inequality of thickness. The vertex, 
to say the least, is as solid a piece of bone as can well be conceived, whilst the sides, 
especially at the temporal region, are quite the reverse of this—namely, a thin plate of 
bone. To specify, and with reference to our figure, the nearly vertical section of the 
frontal bone in this female was above three quarters of an inch deep, the temporal and 
part of the parietal plates little more than a line, the occipital wall less than half an 
inch at its middle, but thicker at the sides. The structure of the bone also varies. 
The frontal is, to an extreme, dense and compact, as, indeed, is the osseous consistence 
generally; only a film of diploé is apparent on the lateral walls, and the occipital 
segment has a distinct (though finely cancellated) interior, with a thin outer vitreous 
table. 
The internal basis cranii examined, as in our figure, with the dura mater retained on 
one moiety, presents a notable difference on the two sides. In that with the membrane 
remaining (the left side, but right of fig. 36, as seen in the Plate) there are two subequal- 
sized oval foss, divided by a nearly transverse arched membranous ridge. 
These correspond respectively to the posterior and middle fosse of, say, the human 
skull. The anterior fossa of Man, in the Manatee is nearly perpendicular, or forms the 
front cranial wall, and hence is only partially visible on looking directly downwards into 
the cranial cavity. Those fossee present in Manatus contain the anterior and posterior 
