344 Veteritiary Obstetrics 



eral intervertebral nerves, each vertebra representing a somite. 

 The buds lengthen to constitute the limbs, the bones arising from 

 the connective tissue, while the muscles develop from the muscle 

 plates of the mesoblast. The segments of the limbs are brought 

 about by transverse grooves where the joints are later to form 

 and the digitations begin as longitudinal grooves, which deepen 

 into clefts. 



Various aberrations in the development of the limits occur in 

 our domestic animals. Merely the buds may appearand, within 

 them, rudimentary bones representing the scapula and pelvis 

 or, more or less also, the humerus and femur, but the other 

 parts may fail of development. Any one, or all, of the 

 limbs may be wanting. Fig. 61 represents the skeleton of a 

 bovine fetus without limbs (Peromelus Apus), while Fig. 62 

 represents a foal, in which the two anterior limbs are wanting 

 (Peromelus Achirus. ) In such cases the defect is apparently 

 due to an arrest in the development of the limb-buds during the 

 first month of pregnanc3\ Between this absence of limbs and 

 their normal development occurs every gradation of arrest in 

 the development of limbs, as peromelus micromelus or dwarf 

 limbs. Rarely a limb may undergo amputation during its early 

 stages of development by becoming involved in a loop of the 

 umbilical cord. 



A more common aberration in the limbs and feet is abnormal 

 fission, by which the entire limb or its digitations become multi- 

 plied. Most commonly, only the digits are involved, resulting 

 in one or more extra digits, as shown in Figs. 63 and 64. 



Sometimes a greater part of the limb is involved in the ab- 

 normal fission. Rarely normal fission fails in those animals nat- 

 urally provided with two or more digits or, after their more or 

 less complete fission, fusion occurs between them and the animal 

 is born with less toes than normal. 



Rarely, in the development of the limbs, a tendency is shown 

 toward the addition of an element not normally present in the 

 genus but regularly occurring in some other genera, as is illustrated 

 in well developed clavicles in the pig, as shown in Fig. 65. 



