Prof. Owen's Description of the Lepidosiren annectens. 333 
imperfect divisions corresponding in number with the upper and lower spines. 
The neurapophyses, or laminæ protecting the spinal chord, are ossified, as 
are also the neural spines and the hæmapophyses and heemal spines* in the 
caudal region. 
The neurapophyses of the atlas are slightly expanded at their lower extre- 
mities, and almost meet below the foramen magnum, where they rest upon the 
anterior pointed extremity of the gelatinous chord; as they ascend, they are 
bent at an open angle, with the upper ends meeting above the foramen mag- 
num: these extremities are disunited, and a short spine is attached to them 
by a ligament. The neurapophyses of the second cervical vertebræ have their 
bases expanded so as to meet below the spinal marrow and above the gela- 
tinous chord ; they are disunited above, as are the rest of the neurapophyses +. 
The basis of these vertebral elements, besides being developed inwards, are 
expanded in the antero-posterior direction so as almost to touch each other; 
they become gradually narrower as they approach the caudal region. The 
neural spines} increase in length from the atlas to the fourth vertebra, and 
are continued of the same length, viz. between four and five lines, to the 
middle of the caudal region, whence they progressively diminish to the end of 
the vertebral column. The supernumerary or dermal spines$ are rather shorter 
than the true vertebral spines, to the upper end of which they are attached by 
ligaments, as in other fishes. In the caudal region they are expanded and 
compressed, and give attachment to the horny transparent filaments which 
support the membrane of the caudal fin: the inferior corresponding ap- 
pendages || of the haemal spines present a similar form, and, like the upper 
ones, have the same bony structure and green colour as the ossified parts of 
the true endo-skeleton. The hæmapophyses** are relatively longer and more 
slender than the neurapophyses. 
The capsule of the anterior extremity of the gelatinous chord is ossified at 
its inferior and lateral parts, where it forms the base of the cranium ; and the 
bodies of the occipital and posterior and anterior sphenoidal vertebrae are 
represented by a single elongated sub-triangular plate of bone++. The base 
* The explanation of these terms, and of the vertebral elements to which they are applied, will be 
found in my paper on the Plesiosaurus macrocephalus, Geol. Trans., 1838. 
+ Tas. XXIII. fig. 4, b.b. t Ib. c. e. $ Ib. d. d. | Ib. g. € 1b. f. 
** Ib. e. tt Ib. 4. fig. 6; and Tas. XXIV. fig. 2, c. 
