POTTHOKK ami KELLEY: OSTEOLOGICAL DEVELOI'MKNT IN SWORDFISH 



centrum 2 and the urostyle at 6.2 mm ENL-9.1 

 mm ESL. Ossification then proceeded from the 

 haemal spine of the preural centrum 2 dorsad to 

 the hypurals. Last to ossify between 16.0 and 17.7 

 mm ESL was hypural 5 (Table 11). The special- 

 ized neural arch of preural centrum 2 began 

 ossification at 7.1-12.3 mm ESL followed by the 

 three epurals. The posteriormostepural was last 

 to ossify between 16.2 and 17.6 mm ESL (Table 

 11). The paired uroneural was not a cartilage 

 bone and it was first present between 9.8 and 

 12.3 mm ESL before epural ossification (Table 

 11). In a few specimens the uroneural had an 

 anomalous shape as if it had fused from two parts 

 (Fig. 22). 



During development of the hypural complex, a 

 parhypurapophysis and a hypurapophysis 

 (Lundberg and Baskin 1969; Nursall 1963) were 

 observed on the parhypural and hypural 1. From 

 a dorsal view the parhypural and hypural 1 are 

 bifurcated as shown in Figure 24. This bifurca- 

 tion can be observed in the adults on the 

 autogenous parhypural but is absent on hypural 

 1, which then is fused to the hypural plate. A 

 tunnellike foramen develops between the tips 

 and rear of the parhypural prezygapophyses for 

 the haemal canal on the proximal surface of the 

 parhypural. This tunnel was not yet developed in 

 a 44.1 mm ESL specimen (Fig. 24) but was fully 

 formed in our 668 mm ESL specimen. 



In adults of Xiphias, hypurals 1-4 fuse with 

 each other and the urostyle, forming a single 

 hypural plate with a notch posteriorly at the 

 center. Grooves present on the plate formed be- 

 cause of articulating rays (Gregory and Conrad 

 1937) (Fig. 23). The epurals, the uroneural, 

 hypural 5, the parhypural, and the haemal spine 

 of preural centrum 2 remained autogenous in the 

 adults. Fusion between hypurals 4 and 3 and 1 

 and 2 started distad from the articular cartilage 

 in an anterior direction at 17.2-26.7 mm ESL 

 (Figs. 21, 22; Table 11). Fusion of the two hypural 

 plates, however, was in a posterior direction 

 starting proximally. We could not determine the 

 size at which the dorsal and ventral hypural 

 plates fused with each other and with the 

 urostyle because of insufficient samples (Fig. 1; 

 Table 11). 



The parhypural and hypurals 1-5 supported 

 the principal caudal rays. Only on one occasion 

 did the haemal spine of preural centrum 2 

 support a principal caudal ray, but this is not 

 shown in Table 12. The distribution of principal 

 rays on the hypural bones can only be seen in 



Haemal 

 Canal 



0.5 mm 



FIGURE 24.— The parhypural and hypural 1 from a 44.1 mm 

 ESL Xiphias gladius. A, dorsal view, enlarged; B, left lateral 

 view. Hyp, hypurapophysis; Phyp, parhypurapophysis. Carti- 

 lage, white; bone, stippled. 



larvae and small juveniles (Figs. 19-22; Table 

 12). 



Table 12.— Distribution of principal caudal 

 rays on the hypurals in 66 Xiphias gladius (8.8- 

 64.6 mm ESL). 



Number of principal caudal rays 



VERTEBRAL COLUMN 



Of 164 Xiphias 5.3 mm ENL-668 mm ESL, 1 

 (0.6%) had 15+10=25 vertebrae, 95 (57.9%) had 

 15+11=26, 65 (39.7%) had 16+10=26, and 3 (1.8%) 

 had 16+11=27 (Nakamura et al. 1968; Ovchin- 

 nikov 1970). 



All centra except the first anteriormost, the 

 urostyle, and preural centrum 2 had neural pre- 

 and postzygapophyses, and neural arches and 

 spines (Figs. 25-27). The first anteriormost 

 centrum lacked a neural prezygapophysis(Figs. 

 13, 27), preural centrum 2 had a neural prezyg- 

 apophysis, a specialized (open) neural arch, and a 

 neural postzygapophysis (Figs. 22, 23). The 

 urostyle had only a neural prezygapophysis 

 (Figs. 21-23). All precaudal vertebrae except the 

 anteriormost had parapophyses (Figs. 13, 25, 



175 



