Prof. Owen's Description of the Lepidosiren annectens. 339 



the higher Vertebrata, so also the extremities retain their simple structure as 

 when they first bud forth, and are devoid of any trace of digital divisions : still 

 the march of development has begun, and we perceive by the numerous joints 

 of the cartilaginous ray, that its direction is towards the ichthyic modification 

 of the great vertebral plan. 



Muscular System*. 



The muscles of the trunk of the Lepidosiren present all the simplicity and 

 uniformity characteristic of the class of Fishes. They are divided by the late- 

 ral line into a dorsal and ventral series, each series consists of narrow subver- 

 tical plates of oblique fibres, separated by intermuscular fasciee which afford 

 on one side attachment to an anterior series, and on the opposite to a poste- 

 rior series of muscular fibres : these fibres are directed upwards and back- 

 wards in the dorsal group, and downwards and backwards in the ventral one : 

 the ventral series occupy the place of the true abdominal muscles which first 

 begin to be developed in the strictly air-breathing Reptiles. The muscles of 

 the mandibular, hyoidean, branchial and scapular arches are represented in 

 Tab. XXIII, and will receive their necessary detailed description in the ex- 

 planation of the figures in that plate. They resemble in some points the 

 arrangement of the same muscles in the Perennibranchians, and in other 

 points that in the true Fishes ; but do not afford any sufficiently characteristic 

 modifications to merit further notice here. It may be also observed, that 

 although the muscles of the trimk are quite fish-like in their disposition, yet 

 that the lower Perennibranchians and the larvie of the higher Batrachia offer 

 a similar agreement in this part of their organization to the class of Fishes. 



Nervous System. 



The brain consists of the following principal masses ; viz. two elongated, 

 oval, subcompressed cerebral lobes, a single elliptical optic lobef, a medulla 

 oblongata:}:, and a transverse medullary fold continued across the anterior 

 part of the widely open fourth ventricle, representing the cerebellum §. In the 

 angle between the representative of the bigeminal bodies and the interspace of 

 the hemispheres there is a well-developed pineal gland || : on the inferior sur- 



* Tab. XXVII. fig. 3 & 4, a a. t lb. fig. 3, b. X lb. fig. 4, c. 



§ lb. fig. 3, d. II lb. fig. 3, e. 



