POTTHOFF and KELLEY: OSTEOLOGKAL DEVELOPMENT IN SWORDFISH 



Table 3.— Development of the pectoral girdle and sus- 

 pensorium for 190 Xiphias gladius (3.7 mm ENL-64.6 mm 

 ESL). length ranges (mm, ENL, or ESL) are from "first ob- 

 servance" to "first observance in all specimens." 



PstCl 



Figure 5.— Left lateral external view of the pectoral girdle 

 and suspensorium from a 187 mm ESL Xiphias gladius. For 

 abbreviations, see Figures 3 and 4. Cartilage, white; ossify- 

 ing, stippled. 



girdle is only briefly mentioned in Gregory and 

 Conrad (1937) and no detailed description is 

 given. 



Our smallest 3.7 mm ENL specimen already 

 had rudiments of a pectoral girdle, consisting of 

 a rod-shaped bony cleithrum, an inverted Y- 

 shaped coraco-scapular cartilage without 

 scapular foramen, and a larval fin blade (similar 

 to the 5.1 mm ENL specimen in Fig. 3) (Table 3). 

 The cleithrum later developed a shelflike dorsal 

 posterior process (Figs. 3-5). The coraco- 

 scapular cartilage at first had long dorsal and 

 long posterior processes and a short anterior 

 process. It developed a foramen on the dorsal 

 process, and the anterior process grew relatively 

 larger and ossified into part of the coracoid, 

 while the posterior process atrophied. Ossifica- 

 tion of the scapula started around the scapular 

 foramen and spread over the dorsal process 

 forming the scapula (Figs. 3, 4; Table 3). The 

 larval fin consisted of two parts: a flat cartilagin- 

 ous semicircular blade surrounded on the cir- 



cumference by a finfold containing larval 

 actinopterygia (Fig. 3). The semicircular carti- 

 laginous pectoral fin blade developed into the 

 four large radials by first forming elongate holes 

 in the blade. These holes then gradually enlarged 

 to the border of the semicircular cartilage blade, 

 forming separate cartilaginous radials, which 

 later ossified (Figs. 3-5; Table 3). 



The pectoral suspensorium, consisting of the 

 posttemporal, supracleithrum, and postclei- 

 thrum, was of dermal origin (did not form from 

 cartilage) and was first seen ossifying at 5.3 mm 

 ENL (Table 3). The posttemporal was at first a 

 flat rectangular bone with spines. The spines 

 were lost and a dorsal and ventral process 

 developed, giving the posttemporal the charac- 

 teristic inverted C shape (Figs. 3-5; Table 3). The 

 supracleithrum was short at first and had spines. 

 It also lost its spines and developed a long pos- 

 terior process which articulated laterally with 

 the posterior process of the cleithrum (Figs. 3-5; 

 Table 3). Lengthening of the supracleithrum 

 accommodates the migration of the pectoral fin 

 from a lateral position in the larvae to a more 

 ventral position in the adults (Ovchinnikov 

 1970). The postcleithrum was an elongate rod- 

 shaped bone without spines from the start and 

 articulated medially with the posterior process 

 of the cleithrum (Figs. 3-5; Table 3). 



DORSAL FIN 



Dorsal fin rays first appeared almost at the 

 same sizes as the anal and caudal rays (Tables 1, 

 4). The dorsal fin rays developed in the dorsal 

 finfold first at the middle of the body above the 

 10th-14th myomere in specimens 5.5-6.1 mm 

 ENL. With growth, addition of dorsal fin rays 



165 



