Prof. Owen's Description of the Lepidosiren annectens. 333 



imperfect divisions corresponding in number with the upper and lower spines. 

 The neurapophyses, or laminae protecting the spinal chord, are ossified, as 

 are also the neural spines and the hsemapophyses 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 vertebrae 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 f. 

 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 appi'oach 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 haemapophyses** 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 ft- 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. 



t Tab. XXIII. fig. 4. b.b. X lb. c.c. § lb. d.d. || lb. g. f lb./. 



** lb. e. tt lb. h. fig. 6 ; and Tab. XXIV. fig. 2, c. 



