334 Prof. Owzw's Description of the Lepidosiren annectens. 
of this plate is turned forwards, the apex expands into an oblique elliptical 
plate, having a shallow depression, which receives the pointed anterior ex- 
tremity of the gelatinous chord. The fibrous capsule of the chord is attached 
to the margin of the basi-occipital depression, and supports the neurapophyses 
of the atlas, anterior to which are the corresponding elements of the occipital 
vertebra itself. These exoccipitals* present the form of thin expanded plates, 
of a subquadrate figure, concave towards the medulla oblongata, which they 
defend and embrace, their anterior and inferior extremities being extended into 
the upper part of the capsule of the fibrous chord, as far as the middle line, like 
the bases of the ordinary neurapophyses : their upper extremities meet above by 
an extended superior margin. The basi-occipital is notched below the base of 
each exoccipital, leaving a foramen for the transmission of a large nerve. The 
limits of the basi-occipital and sphenoid bones are indicated by a transverse 
groove. The basi-sphenoid sends upwards, near its outer margin, two low 
longitudinal vertical plates, which give attachment to the cartilaginous ale 
of the sphenoid forming the lateral parietes of the cranial cavity+. Between 
these ale and the ex-occipital bony pla 
tes is interposed on each side the large 
and thick cartilaginous capsule of the organ of hearing +, which is extended 
upwards to the parietal bone, and represents the petr 
ments of the temporal bone. "There is no distinet supra-occipital bone or spine, 
sa its place is occupied by the posterior extremity of the parietal}. This is 
a single symmetrical, lozenge-shaped bone, from the middle line of whose 
upper surface a longitudinal stout spine is developed, augmenting the surface 
of attachment of the strong temporal muscles. This spine is continued upon 
the frontal bone|| as far as its anterior extremity. Both the parietal and 
frontal bones are ossified, and were anchylosed together in the larger speci- 
men: the limits of the cranial vertebrz are thus effaced above as they are by 
the confluence of the occipital and sphenoids below. The anterior part of the 
fr 3 | : 
ontal is deeply notele on each side. There are no distinct ossified anterior 
frontals, but the posterior frontals€ are 
backwards over the frontal 
ous and squamous ele- 
ä + Th | 
3 Tas. XXIV. fg. 2, K, . XXII s are distinguished by dots in Tan, XXIII. fig. 4. 
$ Ta». XXIII. figs. 4 & 5, k. Ib. . { Ib. mm. 
