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 ichthyie modification 
of the great vertebral plan. 
Muscular System s. 
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 fasciæ 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 
Tas. 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 trunk are quite fish-like in their disposition, yet 
that the lower Perennibranchians and the larvæ 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 lobe f, 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- 
* Tas. XXVII. fig. s & 4, aa. t Ib. fig. 3, b. t Ib. fig. 4, c. 
$ Ib. fig. 3, d. | Ib. fig. 3, e. 
