POTTHOFF anrl KELLEY: OSTEOLOGICAI, DEVELOPMENT IN SWORDFISH 



2 4 6 8 10 12 14 16 18 20 22 24 26 



I I I I I I I 



I I I I I I I I I I I I I I I I 1 



3.7mm 



JUL^- 



4.4mm 



53 mm 



6-2 mm 



7.2 mm 



Figure 29.— Schematic presentation 

 of the vertebral column development 

 in Xiphias gladius. Ticks on scale 

 denote centra number and are 

 aligned with the middle of the 

 centrum. Indicated millimeter mea- 

 surements are ENL or ESL. Carti- 

 lage, white; ossifying, stippled. 



Table 15. — Development of the haemal spines on the anterior 

 to posterior numbered centra for 53 Xiphias gladius 5.0-6.5 

 mm ENL. N - number of specimens, A' = mean. 



larger specimens (Figs. 8, 13, 25, 27). This 

 prezygapophysis is considerably longer than the 

 neural spine except in large juveniles and adults 

 (Fig. 25). 



Ribs developed from a short piece of proximal 

 cartilage. The cartilage later ossified and bone 

 cells were added distally directly in the length- 

 ening process of the rib during development. One 

 pair of ribs was first seen on the anteriormost 

 centrum at 8.0 mm ESL in some specimens. All 

 Xiphias >12.2 mm ESL had at least one pair of 

 ribs developing. Development was in a posterior 

 direction on the first four centra and in an 

 anterior direction on centra 15 and 14. When 



centra 1-3 had developing ribs, usually a pair 

 also was present on centrum 15. Ribs developed 

 over a wide size range. The smallest specimen 

 with a full set of ribs on centra 1-4, 14, and 15 

 measured 25.1 mm ESL and all specimens 

 larger than 55.1 mm ESL had the full rib 

 complement. Xiphias usually developed ribs on 

 centra 1-4, 14, and 15, but a few specimens also 

 had ribs on centra 5, 6, 13, and 16. 



BRANCHIOSTEGAL RAYS 



Branchiostegal rays were first seen in a 4.2 

 mm ENL specimen and all Xiphias >4.2 mm 

 ENL had some rays. The 4.2 mm ENL Xiphias 

 had four rays on each side but a 4.5 mm ENL 

 specimen had only two (Table 16). Branchioste- 

 gals were added from posterior to anterior di- 

 rection, specimens with developing branchios- 

 tegals had either the same count on both sides or 

 differed by one ray between sides. Adult counts 

 of seven or eight rays were first observed at 5.0 

 mm ENL and all Xiphias >6.6 mm ENL had 



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