. Chordate morphology. Morphology (Animals); Chordata. Tui-tjM-riy^ L^. A RUPICAPRA B ANTILOCAPRA D RHINOCEROS F CERVUS Figure 8-5. Horns of different types; their growth and replacement. A, chomois or cow (continuous growth); B, Prong-horned Antilope (shed annually); C, giraffe with knobs of skull covered by skin (continuous growth); D, fibrous or "hair" horn of rhinoceros (continuous growth); E, detail of hairs embedded in matrix of rhinoceros horn; F, bony horn of the deer (shed annually). (After Erdmann, 1934) licles are involved in the origin of the mammary glands, which suggest
. Chordate morphology. Morphology (Animals); Chordata. Tui-tjM-riy^ L^. A RUPICAPRA B ANTILOCAPRA D RHINOCEROS F CERVUS Figure 8-5. Horns of different types; their growth and replacement. A, chomois or cow (continuous growth); B, Prong-horned Antilope (shed annually); C, giraffe with knobs of skull covered by skin (continuous growth); D, fibrous or "hair" horn of rhinoceros (continuous growth); E, detail of hairs embedded in matrix of rhinoceros horn; F, bony horn of the deer (shed annually). (After Erdmann, 1934) licles are involved in the origin of the mammary glands, which suggests that they are modified sebaceous glands. The areolar glands of Montgomery are about interme- diate in form between the apocrine sweat gland and the mammary glands, thus indicating the possibility of transition from sweat to mammary gland. The apocrine sweat glands and sebaceous glands at the edge of the areola of the nipple open together. These glands may have developed from lacta- tion hair follicles. The intergradation of sweat, mammary, and sebaceous glands suggests they are all intimately related. In monotremes, the mammary glands originate from hair follicles that form two bands along the belly of the embryo; these bands are called the milk lines. Mammary develop)- ment is limited to bilateral areas of these strips on the lower part of the belly, and nipples are not formed. The glands open on a pair of bare areas in Ornithorhynchus, and, in the Echidna, into a pair of invaginated pockets lying in the side walls of the marsupium, or pouch. In marsupials, several mammary glands arise from paired invaginations of epidermis along the milk lines on the lower belly. From the bottom of these invaginations, hair follicles develop, and from these, mammary and sebaceous glands arise. Later the hair follicles degenerate, leaving the glands opening into the bottom of the nipple primordeum, which then evaginates. The several pairs of nipples are located in the marsupium. In the mamma
Size: 1766px × 1415px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
