212 SHOULDER-GIRDLE AND BREAST-BONE. 



and fourth " coracoid segments" (Plate XXVII, figs. 11 13, c. s. 1, c. s. 4). The mass of cartilage 

 between these plates becomes rapidly scooped in front ; and in this concavity a simple clavicle (cl.), 

 is formed, at first of a lenticular shape, but afterwards becoming a very solid carpiform bone 

 (see figs. 11 13, my youngest Mole). The manner in which this thick clavicle is imbedded in 

 cartilage is shown in fig. 10 (nearly four diameters) ; it is free in front, and on its outer and inner 

 sides ; but above, below, and behind it is enclosed in the hollowed coracoid cartilage. This hyaline 

 cartilage suffers ossification from the clavicle faster than it grows ; and posteriorly all the cartilage 

 eventually vanishes ; above and below, however, this is persistent, and forms the articular cartilage 

 of the adult (Plate XXVII, figs. 8, 9, cl., c. s. 2, c. s. 3). In the youngest stage, the transformation 

 of the cartilage-cells of the coracoid nearest the bony substance of the clavicle is clearly shown 

 (Plate XXVII, fig. 14, cl., c. s. 2, 150 diameters) ; a tract of fine fibrous tissue is seen separating 

 the persistent cartilage from the upper segment (c. s. 1), which is composed of much smaller cells 

 than the scooped mass ; in the adult the flat segments are composed of longer celled cartilage 

 than that which is attached to the clavicle (Plate XXVII, fig. 9, c. s. 3, c. s. 4). 



The last-quoted figure, which is a slice from the sternal end of the adult Mole's " coraco- 

 clavicle " shows a very clean fissure between the hyaline " meniscus " (c. s. 4) and the hyaline 

 articular cartilage (c. s. 3), but the cavity on the clavicular side of the meniscus is extremely 

 imperfect; in the youngest specimen it appears in some degree (Plate XXVII, fig. 13, between 

 and below c. s. 1, and c. s. 2). The second stage (Plate XXVII, figs. 15 17, three-and-a-half 

 and seven-and-a-half diameters) shows how the clavicular bony matter gains upon the scooped 

 coracoid behind; how that the well-known coracoid foramen (cr. f.) seen also in the adult (fig. 5), 

 pierces the clavicle itself; and the manner in which the lower meniscus spreads out to articulate 

 with the prae-sternum (p. st.) above. I consider that the lowest segments, right and left, are the 

 moieties of a highly modified " omosternum ;" but the other segments answer to much more than 

 those we find in the other Mammalia. In Crocidura (Plate XXVII, figs. 25 and 26, m. sc. s.) 

 the meso-scapular segment is cut through, leaving one part to ossify by itself, and the other to 

 grow on to the clavicle ; in this type the upper meso-scapular piece answers to a fragment of 

 the " first coracoid segment " of the Mole, and the lower to the second ; whilst the distal prse- 

 coracoid (fig. 23, p. cr.) is a small rudiment of the third layer of cartilage in the Mole (Plate 

 XXVII, fig. 8, c. s. 3). The omosternum and epicoracoid of Crocidura (Plate XXVII, fig. 23, 

 o. st., e. cr.) are autogenous rudiments of the great cartilaginous flap which in the Mole articu- 

 lates with the upper surface of the sub-carinate cervical part of the manubrium (Plate XXVII, 

 figs. 4 and 6, cl., p. st. ; and fig. 15, p. st., c. s. 4). 



As a rule, the clavicle is long, slender, and curved in the Insectivora (Plate XXVII, figs. 18 

 and 22 ; and Plate XXVIII, figs. 13, cl.) : in Ennaceus it is stouter (Plate XXV, figs. 16 and 

 19, cl.) ; in this type the mesoscapular segment (fig. 18, m. sc. s.) is partially ossified by the clavicle. 



In ChrysocMoris (Plate XXVII, fig. 18, m. sc. s.) it is a small, but very distinct bone, very 

 independent of the clavicle ; this is illustrated by Crocidura (figs. 22 and 25, m. sc. s.), where it 

 is very distinct from both the acromion and clavicle, and where a secondary part is joined to, 

 and partly ossified by the clavicle. In Sorex tetragonurus the upper part is not cut off from the 

 clavicle (Plate XXVIII, figs. 1 and 4, m. sc. s.) ; it is ossified independently, but feebly, by 

 one large and two smaller endosteal centres. In the Hedgehog the meso-scapular segment and 

 prae-coracoid, which are soft in the young (five or six days old), are separately ossified in the 

 adult ; whilst the omosternum, in the early state, is a mere rod of fibre-cartilage, which is still 



