402 



Family Spalacida (Mole-Rats). 



Genus Bathyergm. 

 Dental formula : i ^, p j=[, m g=20. 



2246. The skeleton of the great Cape Mole-Rat (Batliyergus maritimus). 



In this genus the development of the scalpriform incisors, and of those parts of the skull 

 forming attachments for the muscles that work them, reaches its maximum. The vertebral 

 formula is : 7 cervical, 13 dorsal, 7 lumbar, 4 sacral, and 12 caudal, but the end of the tail 

 is imperfect. The sockets of the inferior incisors are prominent features of the lower jaw, 

 and appear to form the lower border of its rami ; the angles standing outwards and down- 

 wards as broad aliform appendages, with their base of attachment extending from the 

 condyle forwards to beneath the second molar tooth. The atlas has a tubercle both above 

 and below. The axis has a broad compressed spine : the rest of the cervical vertebrae are 

 spineless : the transverse processes of the last (seventh) are imperforate. The accessory 

 tubercle commences above the diapophysis of the fourth dorsal, and rapidly expands, in the 

 six succeeding ones, into a long, broad, compressed plate, overhanging the tubercle of the rib. 

 It divides into the metapophysis and anapophysis on the twelfth vertebra. The anapophyses 

 disappear in the last two lumbar vertebrae. The diapophyses are rudimental in the four an- 

 terior lumbars, and are unusually short in the last two. Six ribs articulate directly with the 

 sternum, which consists of five bones ; the last supporting an ensifonn cartilage. The upper 

 border of the scapula describes an open angle ; its outer surface is nearly equally bisected by 

 the spine, which rises to an unusual height, and sends off a remarkably long subtrihedral 

 acromion, the extremity of which appears as a thick epiphysis bent towards the long and 

 strong clavicles with which it articulates : a well-marked deltoid process stands out from the 

 middle of the shaft of the humerus, which is imperforate at its distal end. The olecranon is 

 unusually thick and expanded. The femur shows a rudiment of a third trochanter. The fibula 

 is anchylosed to the tibia. A remarkable accessory ossicle, articulated to the tarsal os navi- 

 culare, projects inwards like an accessory or sixth digit of the hind foot. As in other bur- 

 rowing animals, the lumbar and pelvic regions are narrow. The occipital region of the skull 

 is very broad and low. The compressed paroccipitals project downwards and backwards. 

 The auditory bulla is pyriform, its apex articulating with the pterygoids. The temporal 

 fossae meet along a well-developed crista extending from the interorbital region to the strong 

 transverse superoccipital crest. The squamosal forms a horizontal plate, with a curved border 

 extending from the root of the zygoma to above the ' meatus externus,' which is directed up- 

 wards and forwards. The zygomatic arches are strongly curved outwards. The premaxil- 

 laries extend further backwards than the nasals : these are very long and narrow. The 

 upper incisors are grooved anteriorly ; the lower incisors are not grooved. 



Mm. South. 



