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



f. Fibrous membrane filling the interspace of the pterygoids and form- 



ing the roof of the mouth. 



g. Papillose mucous membrane of the palate. 

 h. Maxillary dental plate. 



i. Intermaxillary teeth. 

 k. k. Cartilaginous representatives of the ' ossa petrosa,' containing the 



organ of hearing. 

 /. /. Internal stratum of muscular fibres {inter costales), commencing 

 between the ribs, and continued over the upper or dorsal two 

 thirds of the abdominal cavity. A portion (at the interspace of 

 the letters) is dissected away to show the inner surface of the ex- 

 ternal muscular stratum. 

 m. m. Serous layer of the peritoneum : the letters on the right side show 



the line of reflection of this layer from 

 n. n. The glistening fibrous membrane of the abdominal cavity. 

 Fig. 3. The lower jaw, seen from behind, showing the trochlear cavities, o. o., 

 which are adapted to the convexities, e. e. fig. 2. 



4. Under surface of the head of the Lepidosiren, showing the largely-deve- 



loped mylo-hyoideus, a., which is first exposed when the skin is dis- 

 sected away : it arises not only from the rami of the jaw, but from 

 the whole length of the preopercular bone, and is inserted with its 

 fellow in a median raph6 ; it compresses the branchial cavity. 



5. In this figure the preceding muscle is reflected to expose h. the retractor 



of the OS hyoides, which is at the same time, through the attach- 

 ment of the genio-hyoideus, c, a retractor and depressor of the lower 

 jaw. This powerful muscle takes its origin from the median apo- 

 neurosis representing the sternum, and may be regarded as the 

 homologue of the sterno-hyoideus : by retracting the os hyoides it 

 dilates the branchial cavity, and is thus the principal muscle of 

 aquatic inspiration. 



6. Shows the muscles, d. d., which are exposed by the reflection of the 



preceding ones : they are very thick, connect the hyoid with the 

 coracoid arch, and both with the great ventro-lateral series of 

 pauscles. 



