Dissecting Ozbert the ostrich

After last week's look at an emu dissection, it seemed only logical to follow up with dissection pics of another ratite. So when John Hutchinson of the Royal Veterinary College (RVC) mentioned his dissection photos of Ozbert the ostrich, I asked politely, and received. Note that all photos are © John Hutchinson and Jason Moore, and are used with permission. Ozbert's suspended cadaver is shown here [note the gigantic calf muscles and extruded phallus].

Ozbert, donated by a British ostrich farm, was huge, tipping the scales (when plucked) at 129 kg (the world record is supposedly 160 kg) [scales shown below]. Ostrich feathers presumably account for about the same percentage of mass as they do in emus (c. 7.5%), so Ozbert would have been a bit heavier when alive. Ozbert's untimely death came as a result of combat with another male: he was kicked, fatally, at the base of the neck, and you can see the resulting neck injury in one of the photos below. The ability of ostriches to kill lions and hyenas by kicking is pretty well known, and captive specimens have at least tried to kill people in the same way too. Evidently, ostriches can also kill other ostriches. Not surprising given their hindlimb musculature, on which read on...

Before getting to the hindlimb (the focus of interest for the RVC folks), let's note a few other things. Firstly: necks. If you're interested in necks - and I am - those of ostriches are particularly interesting, not least of all because they're one of the longest extant tetrapod necks in existence. There are 17 vertebrae in the ostrich neck, and the way in which they move when the bird bends, raises, or lowers its neck has been of great interest to those with a special interest in this sort of thing (e.g., Dzemski & Christian 2007). There is actually some very neat CT data on ostrich neck movement, and on what happens to the zygapophyses when the neck moves, but it's not published yet. More on this at some stage in the future. Ostriches are well known for being able to swallow large, sometimes strangely shaped, objects. The skin of the ostrich neck is particularly flexible and you may have seen the photos where a guy is sticking his hand down an ostrich's throat: the skin is so pliable that, as he extends his fingers within the throat, it looks like he's wearing a glove.

Here's where - at long, long last - we come back to the weird pectoral girdle. As several readers correctly noted, the ostrich pectoral girdle is weird in that the furcula (or wishbone) is absent and what appear to be two separate, paddle-like elements are fused to the scapulocoracoids. These are accessory ossifications called procoracoid processes, and there has been some controversy as to whether they represent separate elements, or ventral extensions of the scapulae (thanks to Lars Dietz for help here). The forelimb (or wing) bones are long and gracile (note in the image below how long and slender the upper arm is: there is no propatagium in ratites), and the carpometacarpus is tridactyl: rheas also have tridactyl hands, whereas kiwi, cassowaries and emus are all monodactyl (and moa had no hands, or arms, at all). As you can see from the photo here, digits I and II both have claws, but this is only obvious when the feathers have been removed. The fatal injury sustained to the neck base is also visible here...

Finally, we get to the hindlimb. Of incidental interest is the fact that, while many ostrich specimens used in research now originate from the ostrich farming industry, the incidence of hindlimb deformities in captive ostriches is apparently quite high (Hahulski et al. 1999), with one of the commonest deformities being tibiotarsal rotation (where the distal end of the tibiotarsus is rotated such that what should be the anterior surface of the bone faces outwards or nearly so).

Ostrich hindlimb muscles are unbelievable, accounting for about 33% of the animal's total mass (in humans, hindlimb muscle mass accounts for 17-20% of total mass). Ostriches at the RVC lab have served us well; several key papers on ostrich anatomy and biomechanics incorporate data from these animals (Smith et al. 2006, 2007, Jindrich et al. 2007: some of those are available for free here. See also Rubenson et al. 2007). There are about 36 hindlimb muscles: their relations, insertion points and actions were all described by Smith et al. (2006). Here is John, busy dissecting and making observations...

The biggest hindlimb muscle is the gastrocnemius. It has three distinct heads (medial, lateral and caudal), accounts for about 18% of the hindlimb muscle mass, and is of course responsible for ankle extension. Its tendon is one of the biggest and widest in the limb. Owing to the size of the bird and the length of its feet, the flexor tendons that attach to its toes are large (the four main ones are all at least 25 cm long). Their size and hence the ease with which they can be separated and handled means that they are being considered for use in human surgical repairs (Karakurum et al. 2003).

The gastrocnemius is actually pretty unusual among the larger hindlimb muscles in being located in the distal part of the limb: all the other large hindlimb muscles are proximally located, which makes sense given that animals that run quickly want their distal limb segments to be as light as possible [the image above shows the thigh and pelvic musculature. Anterior is to the right. Among others, we can see the iliotibialis lateralis and iliofemoralis externus and, at extreme right, the iliotibialis cranialis]. Muscle size correlates directly with power, so the huge cross-sectional area of the gastrocnemius makes it the most powerful hindlimb muscle (though let's note that other, more proximal muscles also produce a lot of power, like the iliotibialis lateralis and iliofibularis). Ostrich feet are among the most specialised of any bird: they're didactyl (the two toes are III and IV), and digit IV lacks a claw. While I could ramble on at this point and say a lot more, I'm afraid my time is up and I have to move on.

I plan to post more 'annotated' dissection pics in future: if you have photos like those featured here, or those used in the emu article, I'd be very interested in featuring them here on the site. The more exotic the beast, the better. And so, we finish by saying a sincere and hearty thanks to John Hutchinson, Jason Moore, and the other RVC staff involved for the use of these images. And thanks also to Ozbert, for he served us well.

For previous Tet Zoo ratite articles see...

• Cassowaries kick ass
• Struthio's pectoral weirdness
• Yes, it was a kiwi
• 200 years of kiwi research
• Dissecting an emu

Refs - -

Dzemski, G. & Christian, A. 2007. Flexibility along the neck of the ostrich (Struthio camelus) and consequences for the reconstruction of dinosaurs with extreme neck length. Journal of Morphology 268, 701-714.

Hahulski, G., Marchellin-Little, D. J. & Stoskopf, M. K. 1999. Morphologic evaluation of rotated tibiotarsal bones in immature ostriches (Struthio camelus). Journal of Avian Medicine and Surgery 13, 252-260.

Jindrich, D. L., Smith, N. C., Jespers, K. & Wilson, A. M. 2007. Mechanics of cutting maneuvers by ostriches (Struthio camelus). Journal of Experimental Biology 210, 1378-1390.

Karakurum, G., Güleç, A., Büyükbebeci, O. & KaradaÄ, E. 2003. The ostrich: an excellent tendon source for the biomechanical studies. Gülhane Tip Dergisi (Gulhane Medical Journal) 45, 180-181.

Rubenson, J., Lloyd, D. G., Besier, T. F., Heliams, D. B. & Fournier, P. A. 2007. Running in ostriches (Struthio camelus): three-dimensional joint axes alignment and joint kinematics. Journal of Experimental Biology 210, 2748-2562.

Smith, N. C., Payne, R. C., Jespers, K. J. & Wilson, A. M. 2007. Muscle moment arms of pelvic limb muscles of the ostrich (Struthio camelus). Journal of Anatomy 211, 313-324.

- ., Wilson, A. M., Jespers, K. J. & Payne, R. C. 2006. Muscle architecture and functional anatomy of the pelvic limb of the ostrich (Struthio camelus). Journal of Anatomy 209, 765-779.